fix: handle database permission issues in sync migration verification

Sync was blocked because the migration registry table creation required
CREATE TABLE permissions that the database user might not have.

Changes:
- Check if migration registry tables exist before attempting to create them
- Skip creation if table exists and user lacks CREATE permissions
- Use information_schema to reliably check table existence
- Apply same fix to user sync status table creation
- Gracefully handle ALTER TABLE failures for backward compatibility

This allows sync to proceed even if the client is a read-limited database user,
as long as the required tables have already been created by an administrator.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

internal/services/sync/service.go

@@ -553,24 +553,34 @@ func (s *Service) listConnectedDBUsers(mariaDB *gorm.DB) (map[string]struct{}, e
 }
 
 func ensureUserSyncStatusTable(db *gorm.DB) error {
-	if err := db.Exec(`
-		CREATE TABLE IF NOT EXISTS qt_pricelist_sync_status (
-			username VARCHAR(100) NOT NULL,
-			last_sync_at DATETIME NOT NULL,
-			updated_at DATETIME NOT NULL,
-			app_version VARCHAR(64) NULL,
-			PRIMARY KEY (username),
-			INDEX idx_qt_pricelist_sync_status_last_sync (last_sync_at)
-		)
-	`).Error; err != nil {
-		return err
+	// Check if table exists instead of trying to create (avoids permission issues)
+	if !tableExists(db, "qt_pricelist_sync_status") {
+		if err := db.Exec(`
+			CREATE TABLE IF NOT EXISTS qt_pricelist_sync_status (
+				username VARCHAR(100) NOT NULL,
+				last_sync_at DATETIME NOT NULL,
+				updated_at DATETIME NOT NULL,
+				app_version VARCHAR(64) NULL,
+				PRIMARY KEY (username),
+				INDEX idx_qt_pricelist_sync_status_last_sync (last_sync_at)
+			)
+		`).Error; err != nil {
+			return fmt.Errorf("create qt_pricelist_sync_status table: %w", err)
+		}
 	}
 
 	// Backward compatibility for environments where table was created without app_version.
-	return db.Exec(`
-		ALTER TABLE qt_pricelist_sync_status
-		ADD COLUMN IF NOT EXISTS app_version VARCHAR(64) NULL
-	`).Error
+	// Only try to add column if table exists.
+	if tableExists(db, "qt_pricelist_sync_status") {
+		if err := db.Exec(`
+			ALTER TABLE qt_pricelist_sync_status
+			ADD COLUMN IF NOT EXISTS app_version VARCHAR(64) NULL
+		`).Error; err != nil {
+			// Log but don't fail if alter fails (column might already exist)
+			slog.Debug("failed to add app_version column", "error", err)
+		}
+	}
+	return nil
 }
 
 // SyncPricelistItems synchronizes items for a specific pricelist