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/handler/dev_handler_isolation_test.go

@@ -26,18 +26,18 @@ func TestDevHandler_Isolation(t *testing.T) {
 			HTTPClient: &http.Client{
 				Transport: roundTripFunc(func(r *http.Request) (*http.Response, error) {
 					if r.Method == http.MethodGet && r.URL.Path == "/clients" {
-						return httpJSONAny(r, http.StatusOK, []map[string]interface{}{
+						return httpJSONAny(r, http.StatusOK, []map[string]any{
 							{
 								"client_id":                  "client-tenant-a",
 								"client_name":                "App Tenant A",
 								"token_endpoint_auth_method": "none", // PKCE
-								"metadata":                   map[string]interface{}{"tenant_id": "tenant-a"},
+								"metadata":                   map[string]any{"tenant_id": "tenant-a"},
 							},
 							{
 								"client_id":                  "client-tenant-b",
 								"client_name":                "App Tenant B",
 								"token_endpoint_auth_method": "none", // PKCE
-								"metadata":                   map[string]interface{}{"tenant_id": "tenant-b"},
+								"metadata":                   map[string]any{"tenant_id": "tenant-b"},
 							},
 						}), nil
 					}
@@ -47,15 +47,15 @@ func TestDevHandler_Isolation(t *testing.T) {
 						if id == "client-tenant-b" {
 							tenantID = "tenant-b"
 						}
-						return httpJSONAny(r, http.StatusOK, map[string]interface{}{
+						return httpJSONAny(r, http.StatusOK, map[string]any{
 							"client_id":                  id,
 							"client_name":                "App " + id,
 							"token_endpoint_auth_method": "none",
-							"metadata":                   map[string]interface{}{"tenant_id": tenantID},
+							"metadata":                   map[string]any{"tenant_id": tenantID},
 						}), nil
 					}
 					if r.Method == http.MethodPost && r.URL.Path == "/clients" {
-						var body map[string]interface{}
+						var body map[string]any
 						json.NewDecoder(r.Body).Decode(&body)
 						return httpJSONAny(r, http.StatusCreated, body), nil
 					}
@@ -205,7 +205,7 @@ func TestDevHandler_Isolation(t *testing.T) {
 		})
 		app.Put("/api/v1/dev/clients/:id", h.UpdateClient)
 
-		body, _ := json.Marshal(map[string]interface{}{
+		body, _ := json.Marshal(map[string]any{
 			"client_name": "Updated Name",
 		})
 
@@ -235,7 +235,7 @@ func TestDevHandler_Isolation(t *testing.T) {
 		})
 		app.Post("/api/v1/dev/clients", h.CreateClient)
 
-		body, _ := json.Marshal(map[string]interface{}{
+		body, _ := json.Marshal(map[string]any{
 			"client_name":  "New App",
 			"type":         "pkce",
 			"redirectUris": []string{"http://localhost/cb"},