feat(02-01): Drift tables, DAOs, scheduling utility, domain models with tests

- Add Rooms, Tasks, TaskCompletions Drift tables with schema v2 migration
- Create RoomsDao with CRUD, watchAll, watchWithStats, cascade delete, reorder
- Create TasksDao with CRUD, watchInRoom (sorted by due), completeTask, overdue detection
- Implement calculateNextDueDate and catchUpToPresent pure scheduling functions
- Define IntervalType enum (8 types), EffortLevel enum, FrequencyInterval model
- Add formatRelativeDate German formatter and curatedRoomIcons icon list
- Enable PRAGMA foreign_keys in beforeOpen migration strategy
- All 30 unit tests passing (17 scheduling + 6 rooms DAO + 7 tasks DAO)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

test/drift/household_keeper/migration_test.dart

@@ -0,0 +1,62 @@
+// dart format width=80
+// ignore_for_file: unused_local_variable, unused_import
+import 'package:drift/drift.dart';
+import 'package:drift_dev/api/migrations_native.dart';
+import 'package:household_keeper/core/database/database.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'generated/schema.dart';
+
+import 'generated/schema_v1.dart' as v1;
+import 'generated/schema_v2.dart' as v2;
+
+void main() {
+  driftRuntimeOptions.dontWarnAboutMultipleDatabases = true;
+  late SchemaVerifier verifier;
+
+  setUpAll(() {
+    verifier = SchemaVerifier(GeneratedHelper());
+  });
+
+  group('simple database migrations', () {
+    // These simple tests verify all possible schema updates with a simple (no
+    // data) migration. This is a quick way to ensure that written database
+    // migrations properly alter the schema.
+    const versions = GeneratedHelper.versions;
+    for (final (i, fromVersion) in versions.indexed) {
+      group('from $fromVersion', () {
+        for (final toVersion in versions.skip(i + 1)) {
+          test('to $toVersion', () async {
+            final schema = await verifier.schemaAt(fromVersion);
+            final db = AppDatabase(schema.newConnection());
+            await verifier.migrateAndValidate(db, toVersion);
+            await db.close();
+          });
+        }
+      });
+    }
+  });
+
+  // The following template shows how to write tests ensuring your migrations
+  // preserve existing data.
+  // Testing this can be useful for migrations that change existing columns
+  // (e.g. by alterating their type or constraints). Migrations that only add
+  // tables or columns typically don't need these advanced tests. For more
+  // information, see https://drift.simonbinder.eu/migrations/tests/#verifying-data-integrity
+  // TODO: This generated template shows how these tests could be written. Adopt
+  // it to your own needs when testing migrations with data integrity.
+  test('migration from v1 to v2 does not corrupt data', () async {
+    // Add data to insert into the old database, and the expected rows after the
+    // migration.
+    // TODO: Fill these lists
+
+    await verifier.testWithDataIntegrity(
+      oldVersion: 1,
+      newVersion: 2,
+      createOld: v1.DatabaseAtV1.new,
+      createNew: v2.DatabaseAtV2.new,
+      openTestedDatabase: AppDatabase.new,
+      createItems: (batch, oldDb) {},
+      validateItems: (newDb) async {},
+    );
+  });
+}