fix(app): 日历页切换月份后保留选中日期的日记列表

app/lib/features/calendar/bloc/calendar_bloc.dart

@@ -131,8 +131,16 @@ class CalendarBloc extends Bloc<CalendarEvent, CalendarState> {
 
       if (state is CalendarLoaded) {
         final current = state as CalendarLoaded;
+        // 根据当前选中日期查找日记，避免进入页面时空白
+        final dayKey = DateTime(
+          current.selectedDay.year,
+          current.selectedDay.month,
+          current.selectedDay.day,
+        );
+        final selectedJournals = byDate[dayKey] ?? [];
         emit(current.copyWith(
           journalsByDate: byDate,
+          selectedDayJournals: selectedJournals,
           isLoading: false,
         ));
       }