Code Review Optimierungen: Typsicherheit, Scanner-Performance, DB Upgrade Template, Division Guard

lib/database/db_helper.dart

@@ -82,6 +82,9 @@ class DbHelper {
           )
         ''');
       },
+      onUpgrade: (db, oldVersion, newVersion) async {
+        // Hier zukünftige DB-Migrationen einpflegen (z.B. if (oldVersion < 2) ...)
+      },
     );
   }