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/presentation/calendar_providers.dart

@@ -57,10 +57,13 @@ final calendarDayProvider =
       overdueTasks = const [];
     }
 
+    final totalTaskCount = await db.calendarDao.getTaskCount();
+
     return CalendarDayState(
       selectedDate: selectedDate,
       dayTasks: dayTasks,
       overdueTasks: overdueTasks,
+      totalTaskCount: totalTaskCount,
     );
   });
 });