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/hydra_admin_service_test.go

@@ -127,7 +127,7 @@ func TestHydraAdminService_PatchClientStatus(t *testing.T) {
 		assert.Equal(t, "PATCH", r.Method)
 		assert.Equal(t, "application/json-patch+json", r.Header.Get("Content-Type"))
 
-		var payload []map[string]interface{}
+		var payload []map[string]any
 		_ = json.NewDecoder(r.Body).Decode(&payload)
 		assert.Equal(t, "replace", payload[0]["op"])
 		assert.Equal(t, "/metadata/status", payload[0]["path"])
@@ -273,7 +273,7 @@ func TestHydraAdminService_AcceptLoginRequest(t *testing.T) {
 		assert.Equal(t, "/oauth2/auth/requests/login/accept", r.URL.Path)
 		assert.Equal(t, challenge, r.URL.Query().Get("login_challenge"))
 
-		var body map[string]interface{}
+		var body map[string]any
 		_ = json.NewDecoder(r.Body).Decode(&body)
 		assert.Equal(t, subject, body["subject"])