refactor: clean up project structure

- Remove old review reports (keep latest only)
- Move docs/ to deploy/docs-backup/
- Move performance-testing/ to deploy/
- Clean up test output files
- Organize root directory

backend/internal/server/middleware/api_key_auth_google_test.go

@@ -80,6 +80,9 @@ func (f fakeAPIKeyRepo) ClearGroupIDByGroupID(ctx context.Context, groupID int64
 func (f fakeAPIKeyRepo) CountByGroupID(ctx context.Context, groupID int64) (int64, error) {
 	return 0, errors.New("not implemented")
 }
+func (f fakeAPIKeyRepo) CountActiveByGroupID(ctx context.Context, groupID int64) (int64, error) {
+	return 0, errors.New("not implemented")
+}
 func (f fakeAPIKeyRepo) ListKeysByUserID(ctx context.Context, userID int64) ([]string, error) {
 	return nil, errors.New("not implemented")
 }

backend/internal/server/middleware/api_key_auth_test.go

@@ -601,6 +601,9 @@ func (r *stubApiKeyRepo) ResetRateLimitWindows(ctx context.Context, id int64) er
 func (r *stubApiKeyRepo) GetRateLimitData(ctx context.Context, id int64) (*service.APIKeyRateLimitData, error) {
 	return nil, nil
 }
+func (r *stubApiKeyRepo) CountActiveByGroupID(ctx context.Context, groupID int64) (int64, error) {
+	return 0, errors.New("not implemented")
+}
 
 type stubUserSubscriptionRepo struct {
 	getActive      func(ctx context.Context, userID, groupID int64) (*service.UserSubscription, error)

backend/internal/server/middleware/metrics.go

@@ -0,0 +1,47 @@
+// Package middleware provides HTTP middleware for metrics collection.
+package middleware
+
+import (
+	"strconv"
+	"time"
+
+	"github.com/Wei-Shaw/sub2api/internal/pkg/metrics"
+	"github.com/gin-gonic/gin"
+)
+
+// PrometheusMetrics returns a Gin middleware that records Prometheus metrics
+func PrometheusMetrics() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		start := time.Now()
+		path := c.FullPath()
+		if path == "" {
+			path = "unknown"
+		}
+
+		c.Next()
+
+		duration := time.Since(start).Seconds()
+		status := strconv.Itoa(c.Writer.Status())
+
+		// Record HTTP metrics
+		metrics.RecordHTTPRequest(c.Request.Method, path, status, duration)
+	}
+}
+
+// GatewayMetrics returns a Gin middleware that records gateway-specific metrics
+func GatewayMetrics() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		start := time.Now()
+		platform := c.GetString("platform")
+		model := c.GetString("model")
+
+		c.Next()
+
+		duration := time.Since(start).Seconds()
+		status := strconv.Itoa(c.Writer.Status())
+
+		if platform != "" {
+			metrics.RecordGatewayRequest(platform, model, status, duration)
+		}
+	}
+}