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/data/calendar_dao.dart

@@ -165,4 +165,59 @@ class CalendarDao extends DatabaseAccessor<AppDatabase>
     final result = await query.getSingle();
     return result.read(countExp) ?? 0;
   }
+
+  /// Watch ALL active tasks with their rooms.
+  ///
+  /// Used by the pre-population logic to determine which tasks should appear
+  /// on days within their current interval window (before their next due date).
+  Stream<List<TaskWithRoom>> watchAllActiveRecurringTasks() {
+    final query = select(tasks).join([
+      innerJoin(rooms, rooms.id.equalsExp(tasks.roomId)),
+    ]);
+    query.where(tasks.isActive.equals(true));
+    query.orderBy([OrderingTerm.asc(tasks.name)]);
+
+    return query.watch().map((rows) {
+      return rows.map((row) {
+        final task = row.readTable(tasks);
+        final room = row.readTable(rooms);
+        return TaskWithRoom(task: task, roomName: room.name, roomId: room.id);
+      }).toList();
+    });
+  }
+
+  /// Watch ALL active tasks with their rooms, filtered to a specific [roomId].
+  ///
+  /// Room-scoped variant of [watchAllActiveRecurringTasks], used by
+  /// [roomCalendarDayProvider] to pre-populate tasks for a single room.
+  Stream<List<TaskWithRoom>> watchAllActiveRecurringTasksInRoom(int roomId) {
+    final query = select(tasks).join([
+      innerJoin(rooms, rooms.id.equalsExp(tasks.roomId)),
+    ]);
+    query.where(tasks.isActive.equals(true) & tasks.roomId.equals(roomId));
+    query.orderBy([OrderingTerm.asc(tasks.name)]);
+
+    return query.watch().map((rows) {
+      return rows.map((row) {
+        final task = row.readTable(tasks);
+        final room = row.readTable(rooms);
+        return TaskWithRoom(task: task, roomName: room.name, roomId: room.id);
+      }).toList();
+    });
+  }
+
+  /// Watch completions for a given [taskId] within a date range [start]..[end].
+  ///
+  /// Used for period-completion filtering: if a task was completed in the
+  /// current interval window, it should not appear as a pre-populated task.
+  /// [start] is inclusive; [end] is exclusive.
+  Stream<List<TaskCompletion>> watchCompletionsInRange(
+      int taskId, DateTime start, DateTime end) {
+    return (select(taskCompletions)
+          ..where((c) =>
+              c.taskId.equals(taskId) &
+              c.completedAt.isBiggerOrEqualValue(start) &
+              c.completedAt.isSmallerThanValue(end)))
+        .watch();
+  }
 }