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/repository/user_projection_repository.go

@@ -76,7 +76,7 @@ func (r *userProjectionRepository) CountTenantMembers(ctx context.Context, tenan
 	}
 
 	valuePlaceholders := make([]string, 0, len(tenants))
-	args := make([]interface{}, 0, len(tenants)*2)
+	args := make([]any, 0, len(tenants)*2)
 	for _, tenant := range tenants {
 		valuePlaceholders = append(valuePlaceholders, "(?, ?)")
 		args = append(args, strings.TrimSpace(tenant.ID), strings.TrimSpace(tenant.Slug))
@@ -124,6 +124,14 @@ func (r *userProjectionRepository) ReplaceAllFromKratos(ctx context.Context, use
 		}
 
 		if len(users) > 0 {
+			// [FIX] Handle email conflicts before bulk upsert
+			for _, u := range users {
+				if u.Email != "" {
+					// Hard-delete any record with same email but different ID to clear unique constraint
+					_ = tx.Unscoped().Where("email = ? AND id != ?", u.Email, u.ID).Delete(&domain.User{}).Error
+				}
+			}
+
 			if err := tx.Clauses(clause.OnConflict{
 				Columns:   []clause.Column{{Name: "id"}},
 				UpdateAll: true,