feat(user): support fixed UUID registration and enhance bulk import results

- Added support for fixed UUIDs during bulk registration (Search-first + ExternalID mapping)
- Implemented idempotency and visibility restoration for soft-deleted users
- Enhanced bulk upload UI to show 'New/Updated/Unchanged' status and modified fields
- Added logic to reclaim identifiers (login_id) from colliding records
- Added frontend E2E and backend unit tests for UUID integrity and conflict handling
- Fixed i18n, formatting, and mock tests to satisfy code-check
- Applied 'go fix' for 'omitzero' tags and general Go standards

backend/internal/service/relying_party_service.go

@@ -100,7 +100,7 @@ func (s *relyingPartyService) enqueueDefaultRelyingPartyRelations(ctx context.Co
 func (s *relyingPartyService) Create(ctx context.Context, tenantID string, client domain.HydraClient) (*domain.RelyingParty, error) {
 	// 1. Create Client in Hydra
 	if client.Metadata == nil {
-		client.Metadata = make(map[string]interface{})
+		client.Metadata = make(map[string]any)
 	}
 	client.Metadata["tenant_id"] = tenantID