feat(11-02): add DAO queries, update CalendarDayState, implement pre-population provider

- Add watchAllActiveRecurringTasks() and watchAllActiveRecurringTasksInRoom() to CalendarDao
- Add watchCompletionsInRange() for period-completion filtering
- Extend CalendarDayState with prePopulatedTasks field (default empty, backward compat)
- Update isEmpty getter to include prePopulatedTasks.isEmpty
- Add _isInCurrentIntervalWindow() and _calculatePreviousDueDate() helpers
- Rewrite calendarDayProvider and roomCalendarDayProvider with pre-population logic
- Fix _subtractMonths() year-boundary bug using total-month arithmetic
- Add 9 new DAO tests for watchAllActiveRecurringTasks, watchAllActiveRecurringTasksInRoom, watchCompletionsInRange

lib/features/home/domain/calendar_models.dart

@@ -1,11 +1,17 @@
 import 'package:household_keeper/features/home/domain/daily_plan_models.dart';
 
-/// State for the calendar day view: tasks for the selected date + overdue tasks.
+/// State for the calendar day view: tasks for the selected date + overdue tasks
+/// + pre-populated tasks within the current interval window.
 class CalendarDayState {
   final DateTime selectedDate;
   final List<TaskWithRoom> dayTasks;
   final List<TaskWithRoom> overdueTasks;
 
+  /// Tasks visible via pre-population: recurring tasks whose nextDueDate is in
+  /// the future but whose current interval window includes [selectedDate].
+  /// These are shown with muted styling to distinguish them from due-today tasks.
+  final List<TaskWithRoom> prePopulatedTasks;
+
   /// Total number of tasks in the database (across all days/rooms).
   /// Used by the UI to distinguish first-run empty state (no tasks exist at all)
   /// from celebration state (tasks exist but today's are all done).
@@ -15,11 +21,11 @@ class CalendarDayState {
     required this.selectedDate,
     required this.dayTasks,
     required this.overdueTasks,
+    this.prePopulatedTasks = const [],
     required this.totalTaskCount,
   });
 
-  /// True when both day tasks and overdue tasks are empty.
-  /// Determined by the UI layer (completion state vs. no tasks at all
-  /// is handled in the widget based on this flag and history context).
-  bool get isEmpty => dayTasks.isEmpty && overdueTasks.isEmpty;
+  /// True when day tasks, overdue tasks, and pre-populated tasks are all empty.
+  bool get isEmpty =>
+      dayTasks.isEmpty && overdueTasks.isEmpty && prePopulatedTasks.isEmpty;
 }