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/backchannel_logout_service_test.go

@@ -36,13 +36,13 @@ func TestBackchannelLogoutService_BuildLogoutToken(t *testing.T) {
 	require.NoError(t, err)
 
 	var claims struct {
-		Issuer  string                 `json:"iss"`
-		Subject string                 `json:"sub"`
-		Aud     interface{}            `json:"aud"`
-		Iat     int64                  `json:"iat"`
-		Jti     string                 `json:"jti"`
-		Sid     string                 `json:"sid"`
-		Events  map[string]interface{} `json:"events"`
+		Issuer  string         `json:"iss"`
+		Subject string         `json:"sub"`
+		Aud     any            `json:"aud"`
+		Iat     int64          `json:"iat"`
+		Jti     string         `json:"jti"`
+		Sid     string         `json:"sid"`
+		Events  map[string]any `json:"events"`
 	}
 	require.NoError(t, parsed.Claims(jwks.Keys[0].Key, &claims))
 
@@ -51,7 +51,7 @@ func TestBackchannelLogoutService_BuildLogoutToken(t *testing.T) {
 	switch aud := claims.Aud.(type) {
 	case string:
 		assert.Equal(t, "client-1", aud)
-	case []interface{}:
+	case []any:
 		assert.Len(t, aud, 1)
 		assert.Equal(t, "client-1", aud[0])
 	default: