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>

lib/core/database/database.dart

@@ -2,14 +2,75 @@ import 'package:drift/drift.dart';
 import 'package:drift_flutter/drift_flutter.dart';
 import 'package:path_provider/path_provider.dart';
 
+import '../../features/rooms/data/rooms_dao.dart';
+import '../../features/tasks/data/tasks_dao.dart';
+import '../../features/tasks/domain/effort_level.dart';
+import '../../features/tasks/domain/frequency.dart';
+
 part 'database.g.dart';
 
-@DriftDatabase(tables: [])
+/// Rooms table: each room has a name, icon, and sort order.
+class Rooms extends Table {
+  IntColumn get id => integer().autoIncrement()();
+  TextColumn get name => text().withLength(min: 1, max: 100)();
+  TextColumn get iconName => text()();
+  IntColumn get sortOrder => integer().withDefault(const Constant(0))();
+  DateTimeColumn get createdAt =>
+      dateTime().clientDefault(() => DateTime.now())();
+}
+
+/// Tasks table: each task belongs to a room and has scheduling info.
+class Tasks extends Table {
+  IntColumn get id => integer().autoIncrement()();
+  IntColumn get roomId => integer().references(Rooms, #id)();
+  TextColumn get name => text().withLength(min: 1, max: 200)();
+  TextColumn get description => text().nullable()();
+  IntColumn get intervalType => intEnum<IntervalType>()();
+  IntColumn get intervalDays =>
+      integer().withDefault(const Constant(1))();
+  IntColumn get anchorDay => integer().nullable()();
+  IntColumn get effortLevel => intEnum<EffortLevel>()();
+  DateTimeColumn get nextDueDate => dateTime()();
+  DateTimeColumn get createdAt =>
+      dateTime().clientDefault(() => DateTime.now())();
+}
+
+/// TaskCompletions table: records when a task was completed.
+class TaskCompletions extends Table {
+  IntColumn get id => integer().autoIncrement()();
+  IntColumn get taskId => integer().references(Tasks, #id)();
+  DateTimeColumn get completedAt => dateTime()();
+}
+
+@DriftDatabase(
+  tables: [Rooms, Tasks, TaskCompletions],
+  daos: [RoomsDao, TasksDao],
+)
 class AppDatabase extends _$AppDatabase {
-  AppDatabase([QueryExecutor? executor]) : super(executor ?? _openConnection());
+  AppDatabase([QueryExecutor? executor])
+      : super(executor ?? _openConnection());
 
   @override
-  int get schemaVersion => 1;
+  int get schemaVersion => 2;
+
+  @override
+  MigrationStrategy get migration {
+    return MigrationStrategy(
+      onCreate: (Migrator m) async {
+        await m.createAll();
+      },
+      onUpgrade: (Migrator m, int from, int to) async {
+        if (from < 2) {
+          await m.createTable(rooms);
+          await m.createTable(tasks);
+          await m.createTable(taskCompletions);
+        }
+      },
+      beforeOpen: (details) async {
+        await customStatement('PRAGMA foreign_keys = ON');
+      },
+    );
+  }
 
   static QueryExecutor _openConnection() {
     return driftDatabase(