fix: remove dead SchemaMigrationService and unused Migration entity

src/config/datasource.ts

@@ -6,14 +6,10 @@ export const AppDataSource = new DataSource({
   synchronize: false,
   // Load all entity files so schema-aware operations (migration:run,
   // migration:generate, the drift check) can compare the database against the
-  // actual entity definitions. `!(migrations|modules)` excludes TypeORM
-  // helpers under src/migrations and the (non-compiling, unregistered)
-  // src/modules entities.
+  // actual entity definitions. `!(migrations|modules)` excludes the
+  // (non-compiling, unregistered) src/modules entities.
   entities: ['src/!(migrations|modules)/**/*.entity.ts'],
-  // Match only timestamp-prefixed migration files. This deliberately excludes
-  // non-migration helpers that live under src/migrations (e.g.
-  // schema-migration.service.ts and the entities/ subdir) which TypeORM would
-  // otherwise try to load as migrations and reject.
+  // Match only timestamp-prefixed migration files.
   migrations: ['src/migrations/[0-9]*.{ts,js}'],
   migrationsTableName: 'migrations',
 });