feat(07-01): integrate sort logic into calendarDayProvider and tasksInRoomProvider

- calendarDayProvider watches sortPreferenceProvider and sorts dayTasks
- overdueTasks intentionally unsorted (pinned at top per design decision)
- tasksInRoomProvider watches sortPreferenceProvider and sorts via stream.map
- _sortTasks helper (TaskWithRoom) and _sortTasksRaw helper (Task) both support:
  - alphabetical: case-insensitive A-Z by name
  - interval: by intervalType.index ascending, intervalDays as tiebreaker
  - effort: by effortLevel.index ascending (low→medium→high)
- All 113 tests pass, analyze clean

lib/features/tasks/presentation/task_providers.dart

@@ -6,17 +6,44 @@ import 'package:household_keeper/core/database/database.dart';
 import 'package:household_keeper/core/providers/database_provider.dart';
 import 'package:household_keeper/features/tasks/domain/effort_level.dart';
 import 'package:household_keeper/features/tasks/domain/frequency.dart';
+import 'package:household_keeper/features/tasks/domain/task_sort_option.dart';
+import 'package:household_keeper/features/tasks/presentation/sort_preference_notifier.dart';
 
 part 'task_providers.g.dart';
 
-/// Stream provider family for tasks in a specific room, sorted by due date.
+/// Sort a list of [Task] by the given [sortOption].
+///
+/// Returns a new sorted list; never mutates the original.
+List<Task> _sortTasksRaw(List<Task> tasks, TaskSortOption sortOption) {
+  final sorted = List<Task>.from(tasks);
+  switch (sortOption) {
+    case TaskSortOption.alphabetical:
+      sorted.sort((a, b) => a.name.toLowerCase().compareTo(
+            b.name.toLowerCase(),
+          ));
+    case TaskSortOption.interval:
+      sorted.sort((a, b) {
+        final cmp = a.intervalType.index.compareTo(b.intervalType.index);
+        if (cmp != 0) return cmp;
+        return a.intervalDays.compareTo(b.intervalDays);
+      });
+    case TaskSortOption.effort:
+      sorted.sort((a, b) => a.effortLevel.index.compareTo(b.effortLevel.index));
+  }
+  return sorted;
+}
+
+/// Stream provider family for tasks in a specific room, sorted by active sort preference.
 ///
 /// Defined manually because riverpod_generator has trouble with drift's
 /// generated [Task] type in family provider return types.
 final tasksInRoomProvider =
     StreamProvider.family.autoDispose<List<Task>, int>((ref, roomId) {
   final db = ref.watch(appDatabaseProvider);
-  return db.tasksDao.watchTasksInRoom(roomId);
+  final sortOption = ref.watch(sortPreferenceProvider);
+  return db.tasksDao
+      .watchTasksInRoom(roomId)
+      .map((tasks) => _sortTasksRaw(tasks, sortOption));
 });
 
 /// Notifier for task mutations: create, update, delete, complete.