fix: resolve all P0/P1 code quality issues

P0 fixes:
- P0-01: sticky_session_test.go add context import
- P0-02: wire_gen.go add usageLogRepository parameter
- P0-03: admin_service_stub_test.go add GetGroupAPIKeyCount
- P0-04: admin_basic_handlers_test.go add stubUsageLogRepository

P1 fixes:
- P1-03: group_handler.go GetStats implement real data query

E2E fixes:
- Fix API Key path to /api/v1/keys (user endpoint)

Documentation:
- Update MEMORY.md with latest fixes

backend/internal/handler/admin/admin_basic_handlers_test.go

@@ -17,7 +17,7 @@ func setupAdminRouter() (*gin.Engine, *stubAdminService) {
 	adminSvc := newStubAdminService()
 
 	userHandler := NewUserHandler(adminSvc, nil)
-	groupHandler := NewGroupHandler(adminSvc, nil, nil)
+	groupHandler := NewGroupHandler(adminSvc, nil, nil, &stubUsageLogRepository{})
 	proxyHandler := NewProxyHandler(adminSvc)
 	redeemHandler := NewRedeemHandler(adminSvc, nil)
 

backend/internal/handler/admin/admin_service_stub_test.go

@@ -6,6 +6,8 @@ import (
 	"sync"
 	"time"
 
+	"github.com/Wei-Shaw/sub2api/internal/pkg/pagination"
+	"github.com/Wei-Shaw/sub2api/internal/pkg/usagestats"
 	"github.com/Wei-Shaw/sub2api/internal/service"
 )
 
@@ -175,6 +177,10 @@ func (s *stubAdminService) GetGroupAPIKeys(ctx context.Context, groupID int64, p
 	return s.apiKeys, int64(len(s.apiKeys)), nil
 }
 
+func (s *stubAdminService) GetGroupAPIKeyCount(_ context.Context, _ int64) (int64, error) {
+	return int64(len(s.apiKeys)), nil
+}
+
 func (s *stubAdminService) GetGroupRateMultipliers(_ context.Context, _ int64) ([]service.UserGroupRateEntry, error) {
 	return nil, nil
 }
@@ -451,3 +457,120 @@ func (s *stubAdminService) ReplaceUserGroup(ctx context.Context, userID, oldGrou
 
 // Ensure stub implements interface.
 var _ service.AdminService = (*stubAdminService)(nil)
+var _ service.UsageLogRepository = (*stubUsageLogRepository)(nil)
+
+// stubUsageLogRepository is a minimal no-op stub for service.UsageLogRepository used in handler tests.
+type stubUsageLogRepository struct{}
+
+func (s *stubUsageLogRepository) Create(ctx context.Context, log *service.UsageLog) (bool, error) {
+	return true, nil
+}
+func (s *stubUsageLogRepository) GetByID(ctx context.Context, id int64) (*service.UsageLog, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) Delete(ctx context.Context, id int64) error { return nil }
+func (s *stubUsageLogRepository) ListByUser(ctx context.Context, userID int64, params pagination.PaginationParams) ([]service.UsageLog, *pagination.PaginationResult, error) {
+	return nil, nil, nil
+}
+func (s *stubUsageLogRepository) ListByAPIKey(ctx context.Context, apiKeyID int64, params pagination.PaginationParams) ([]service.UsageLog, *pagination.PaginationResult, error) {
+	return nil, nil, nil
+}
+func (s *stubUsageLogRepository) ListByAccount(ctx context.Context, accountID int64, params pagination.PaginationParams) ([]service.UsageLog, *pagination.PaginationResult, error) {
+	return nil, nil, nil
+}
+func (s *stubUsageLogRepository) ListByUserAndTimeRange(ctx context.Context, userID int64, startTime, endTime time.Time) ([]service.UsageLog, *pagination.PaginationResult, error) {
+	return nil, nil, nil
+}
+func (s *stubUsageLogRepository) ListByAPIKeyAndTimeRange(ctx context.Context, apiKeyID int64, startTime, endTime time.Time) ([]service.UsageLog, *pagination.PaginationResult, error) {
+	return nil, nil, nil
+}
+func (s *stubUsageLogRepository) ListByAccountAndTimeRange(ctx context.Context, accountID int64, startTime, endTime time.Time) ([]service.UsageLog, *pagination.PaginationResult, error) {
+	return nil, nil, nil
+}
+func (s *stubUsageLogRepository) ListByModelAndTimeRange(ctx context.Context, modelName string, startTime, endTime time.Time) ([]service.UsageLog, *pagination.PaginationResult, error) {
+	return nil, nil, nil
+}
+func (s *stubUsageLogRepository) GetAccountWindowStats(ctx context.Context, accountID int64, startTime time.Time) (*usagestats.AccountStats, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetAccountTodayStats(ctx context.Context, accountID int64) (*usagestats.AccountStats, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetDashboardStats(ctx context.Context) (*usagestats.DashboardStats, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetUsageTrendWithFilters(ctx context.Context, startTime, endTime time.Time, granularity string, userID, apiKeyID, accountID, groupID int64, model string, requestType *int16, stream *bool, billingType *int8) ([]usagestats.TrendDataPoint, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetModelStatsWithFilters(ctx context.Context, startTime, endTime time.Time, userID, apiKeyID, accountID, groupID int64, requestType *int16, stream *bool, billingType *int8) ([]usagestats.ModelStat, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetEndpointStatsWithFilters(ctx context.Context, startTime, endTime time.Time, userID, apiKeyID, accountID, groupID int64, model string, requestType *int16, stream *bool, billingType *int8) ([]usagestats.EndpointStat, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetUpstreamEndpointStatsWithFilters(ctx context.Context, startTime, endTime time.Time, userID, apiKeyID, accountID, groupID int64, model string, requestType *int16, stream *bool, billingType *int8) ([]usagestats.EndpointStat, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetGroupStatsWithFilters(ctx context.Context, startTime, endTime time.Time, userID, apiKeyID, accountID, groupID int64, requestType *int16, stream *bool, billingType *int8) ([]usagestats.GroupStat, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetUserBreakdownStats(ctx context.Context, startTime, endTime time.Time, dim usagestats.UserBreakdownDimension, limit int) ([]usagestats.UserBreakdownItem, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetAllGroupUsageSummary(ctx context.Context, todayStart time.Time) ([]usagestats.GroupUsageSummary, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetAPIKeyUsageTrend(ctx context.Context, startTime, endTime time.Time, granularity string, limit int) ([]usagestats.APIKeyUsageTrendPoint, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetUserUsageTrend(ctx context.Context, startTime, endTime time.Time, granularity string, limit int) ([]usagestats.UserUsageTrendPoint, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetUserSpendingRanking(ctx context.Context, startTime, endTime time.Time, limit int) (*usagestats.UserSpendingRankingResponse, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetBatchUserUsageStats(ctx context.Context, userIDs []int64, startTime, endTime time.Time) (map[int64]*usagestats.BatchUserUsageStats, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetBatchAPIKeyUsageStats(ctx context.Context, apiKeyIDs []int64, startTime, endTime time.Time) (map[int64]*usagestats.BatchAPIKeyUsageStats, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetUserDashboardStats(ctx context.Context, userID int64) (*usagestats.UserDashboardStats, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetAPIKeyDashboardStats(ctx context.Context, apiKeyID int64) (*usagestats.UserDashboardStats, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetUserUsageTrendByUserID(ctx context.Context, userID int64, startTime, endTime time.Time, granularity string) ([]usagestats.TrendDataPoint, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetUserModelStats(ctx context.Context, userID int64, startTime, endTime time.Time) ([]usagestats.ModelStat, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) ListWithFilters(ctx context.Context, params pagination.PaginationParams, filters usagestats.UsageLogFilters) ([]service.UsageLog, *pagination.PaginationResult, error) {
+	return nil, nil, nil
+}
+func (s *stubUsageLogRepository) GetGlobalStats(ctx context.Context, startTime, endTime time.Time) (*usagestats.UsageStats, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetStatsWithFilters(ctx context.Context, filters usagestats.UsageLogFilters) (*usagestats.UsageStats, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetAccountUsageStats(ctx context.Context, accountID int64, startTime, endTime time.Time) (*usagestats.AccountUsageStatsResponse, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetUserStatsAggregated(ctx context.Context, userID int64, startTime, endTime time.Time) (*usagestats.UsageStats, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetAPIKeyStatsAggregated(ctx context.Context, apiKeyID int64, startTime, endTime time.Time) (*usagestats.UsageStats, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetAccountStatsAggregated(ctx context.Context, accountID int64, startTime, endTime time.Time) (*usagestats.UsageStats, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetModelStatsAggregated(ctx context.Context, modelName string, startTime, endTime time.Time) (*usagestats.UsageStats, error) {
+	return nil, nil
+}
+func (s *stubUsageLogRepository) GetDailyStatsAggregated(ctx context.Context, userID int64, startTime, endTime time.Time) ([]map[string]any, error) {
+	return nil, nil
+}

backend/internal/handler/admin/group_handler.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/Wei-Shaw/sub2api/internal/handler/dto"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/response"
@@ -20,6 +21,7 @@ type GroupHandler struct {
 	adminService         service.AdminService
 	dashboardService     *service.DashboardService
 	groupCapacityService *service.GroupCapacityService
+	usageLogRepo         service.UsageLogRepository
 }
 
 type optionalLimitField struct {
@@ -72,11 +74,12 @@ func (f optionalLimitField) ToServiceInput() *float64 {
 }
 
 // NewGroupHandler creates a new admin group handler
-func NewGroupHandler(adminService service.AdminService, dashboardService *service.DashboardService, groupCapacityService *service.GroupCapacityService) *GroupHandler {
+func NewGroupHandler(adminService service.AdminService, dashboardService *service.DashboardService, groupCapacityService *service.GroupCapacityService, usageLogRepo service.UsageLogRepository) *GroupHandler {
 	return &GroupHandler{
 		adminService:         adminService,
 		dashboardService:     dashboardService,
 		groupCapacityService: groupCapacityService,
+		usageLogRepo:         usageLogRepo,
 	}
 }
 
@@ -358,14 +361,48 @@ func (h *GroupHandler) GetStats(c *gin.Context) {
 		return
 	}
 
-	// Return mock data for now
+	ctx := c.Request.Context()
+
+	// Get group info
+	group, err := h.adminService.GetGroup(ctx, groupID)
+	if err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+
+	// Get API key count
+	totalAPIKeys, err := h.adminService.GetGroupAPIKeyCount(ctx, groupID)
+	if err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+
+	// Get today's usage stats
+	now := time.Now()
+	startOfDay := time.Date(now.Year(), now.Month(), now.Day(), 0, 0, 0, 0, now.Location())
+
+	stats, err := h.usageLogRepo.GetGroupStatsWithFilters(ctx, startOfDay, now, 0, 0, 0, groupID, nil, nil, nil)
+	if err != nil {
+		response.ErrorFrom(c, err)
+		return
+	}
+
+	// Calculate totals from stats
+	var totalRequests int64
+	var totalCost float64
+	for _, s := range stats {
+		totalRequests += s.Requests
+		totalCost += s.ActualCost
+	}
+
 	response.Success(c, gin.H{
-		"total_api_keys":  0,
-		"active_api_keys": 0,
-		"total_requests":  0,
-		"total_cost":      0.0,
+		"id":               group.ID,
+		"name":             group.Name,
+		"total_api_keys":  totalAPIKeys,
+		"active_api_keys": totalAPIKeys, // All keys in group are considered active
+		"total_requests":  totalRequests,
+		"total_cost":       totalCost,
 	})
-	_ = groupID // TODO: implement actual stats
 }
 
 // GetUsageSummary returns today's and cumulative cost for all groups.

backend/internal/handler/wire.go

@@ -70,6 +70,16 @@ func ProvideSettingHandler(settingService *service.SettingService, buildInfo Bui
 	return NewSettingHandler(settingService, buildInfo.Version)
 }
 
+// ProvideGroupHandler creates GroupHandler with all dependencies
+func ProvideGroupHandler(
+	adminService service.AdminService,
+	dashboardService *service.DashboardService,
+	groupCapacityService *service.GroupCapacityService,
+	usageLogRepo service.UsageLogRepository,
+) *admin.GroupHandler {
+	return admin.NewGroupHandler(adminService, dashboardService, groupCapacityService, usageLogRepo)
+}
+
 // ProvideHandlers creates the Handlers struct
 func ProvideHandlers(
 	authHandler *AuthHandler,
@@ -126,7 +136,7 @@ var ProviderSet = wire.NewSet(
 	// Admin handlers
 	admin.NewDashboardHandler,
 	admin.NewUserHandler,
-	admin.NewGroupHandler,
+	ProvideGroupHandler,
 	admin.NewAccountHandler,
 	admin.NewAnnouncementHandler,
 	admin.NewDataManagementHandler,