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_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)