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/features/rooms/domain/room_icons.dart

@@ -0,0 +1,40 @@
+import 'package:flutter/material.dart';
+
+/// Curated list of ~25 household Material Icons for the room icon picker.
+const List<({String name, IconData icon})> curatedRoomIcons = [
+  (name: 'kitchen', icon: Icons.kitchen),
+  (name: 'bathtub', icon: Icons.bathtub),
+  (name: 'bed', icon: Icons.bed),
+  (name: 'living', icon: Icons.living),
+  (name: 'weekend', icon: Icons.weekend),
+  (name: 'door_front', icon: Icons.door_front_door),
+  (name: 'desk', icon: Icons.desk),
+  (name: 'garage', icon: Icons.garage),
+  (name: 'balcony', icon: Icons.balcony),
+  (name: 'local_laundry', icon: Icons.local_laundry_service),
+  (name: 'stairs', icon: Icons.stairs),
+  (name: 'child_care', icon: Icons.child_care),
+  (name: 'single_bed', icon: Icons.single_bed),
+  (name: 'dining', icon: Icons.dining),
+  (name: 'yard', icon: Icons.yard),
+  (name: 'grass', icon: Icons.grass),
+  (name: 'home', icon: Icons.home),
+  (name: 'storage', icon: Icons.inventory_2),
+  (name: 'window', icon: Icons.window),
+  (name: 'cleaning', icon: Icons.cleaning_services),
+  (name: 'iron', icon: Icons.iron),
+  (name: 'microwave', icon: Icons.microwave),
+  (name: 'shower', icon: Icons.shower),
+  (name: 'chair', icon: Icons.chair),
+  (name: 'door_sliding', icon: Icons.door_sliding),
+];
+
+/// Map a stored icon name string back to its IconData.
+///
+/// Returns [Icons.home] as fallback if the name is not found.
+IconData mapIconName(String name) {
+  for (final entry in curatedRoomIcons) {
+    if (entry.name == name) return entry.icon;
+  }
+  return Icons.home;
+}