feat(05-02): build CalendarStrip, CalendarTaskRow, CalendarDayList widgets

- Add totalTaskCount field to CalendarDayState to distinguish first-run from celebration
- Add getTaskCount() to CalendarDao (SELECT COUNT from tasks)
- CalendarStrip: 181-day horizontal scroll with German abbreviations, today highlighting, month boundary labels, scroll-to-today controller
- CalendarTaskRow: task name + room tag chip + checkbox, no relative date, isOverdue coral styling
- CalendarDayList: loading/error/first-run-empty/empty-day/celebration/has-tasks states, overdue section (today only), slide-out completion animation
- Update home_screen_test.dart and app_shell_test.dart to test new calendar providers instead of dailyPlanProvider

lib/features/home/data/calendar_dao.dart

@@ -45,6 +45,16 @@ class CalendarDao extends DatabaseAccessor<AppDatabase>
     });
   }
 
+  /// Returns the total count of tasks across all rooms and dates.
+  ///
+  /// Used by the UI to distinguish first-run empty state from celebration state.
+  Future<int> getTaskCount() async {
+    final countExp = tasks.id.count();
+    final query = selectOnly(tasks)..addColumns([countExp]);
+    final result = await query.getSingle();
+    return result.read(countExp) ?? 0;
+  }
+
   /// Watch tasks whose [nextDueDate] is strictly before [referenceDate].
   ///
   /// Returns tasks sorted by [nextDueDate] ascending (oldest first).