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")
 }