feat(app): BLoC 集成 Repository + SettingsBloc 主题切换

全局依赖注入:
- app.dart 注入 JournalRepository + ClassRepository + SettingsBloc
- ApiClient token 自动注入（监听 AuthBloc 状态）

BLoC 重构 (占位数据 → Repository):
- CalendarBloc: 通过 JournalRepository 加载月度日记
- ClassBloc: 通过 ClassRepository + JournalRepository 加载班级数据
- 新增 ClassJoin 事件支持班级码加入
- HomeBloc: 加载最近日记 + 心情概览 + 连续天数 + 今日是否已写

设置系统:
- SettingsBloc: ThemeMode 切换 (system/light/dark)
- app.dart 通过 ListenableBuilder 响应主题变化
- HomeBloc 支持下拉刷新

首页增强:
- 连续天数徽章 + 今日已写标记 + 最常用心情高亮
- RefreshIndicator 下拉刷新
- 日记列表卡片显示日期

验证: flutter analyze 0 error

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

@@ -1,7 +1,8 @@
-// 日历 BLoC — 管理日历视图状态和日记列表
+// 日历 BLoC — 管理日历视图状态，通过 JournalRepository 加载数据
 
 import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:nuanji_app/data/models/journal_entry.dart';
+import 'package:nuanji_app/data/repositories/journal_repository.dart';
 
 // ===== Events =====
 
@@ -21,18 +22,12 @@ final class CalendarDaySelected extends CalendarEvent {
   const CalendarDaySelected(this.day);
 }
 
-/// 切换视图模式（月/周/时间轴）
+/// 切换视图模式
 final class CalendarViewModeChanged extends CalendarEvent {
   final CalendarViewMode mode;
   const CalendarViewModeChanged(this.mode);
 }
 
-/// 加载某月的日记列表
-final class CalendarLoadJournals extends CalendarEvent {
-  final DateTime month;
-  const CalendarLoadJournals(this.month);
-}
-
 // ===== State =====
 
 /// 日历视图模式
@@ -43,29 +38,17 @@ sealed class CalendarState {
   const CalendarState();
 }
 
-/// 初始加载中
 final class CalendarInitial extends CalendarState {
   const CalendarInitial();
 }
 
-/// 日历已加载 — 包含当前月份、选中日期、日记列表
+/// 日历已加载
 final class CalendarLoaded extends CalendarState {
-  /// 当前显示的月份
   final DateTime focusedMonth;
-
-  /// 选中的日期
   final DateTime selectedDay;
-
-  /// 当前月份所有日记（按日期索引）
   final Map<DateTime, List<JournalEntry>> journalsByDate;
-
-  /// 当前选中日期的日记列表
   final List<JournalEntry> selectedDayJournals;
-
-  /// 视图模式
   final CalendarViewMode viewMode;
-
-  /// 是否正在加载
   final bool isLoading;
 
   const CalendarLoaded({
@@ -95,7 +78,6 @@ final class CalendarLoaded extends CalendarState {
       );
 }
 
-/// 加载失败
 final class CalendarError extends CalendarState {
   final String message;
   const CalendarError(this.message);
@@ -104,17 +86,20 @@ final class CalendarError extends CalendarState {
 // ===== BLoC =====
 
 class CalendarBloc extends Bloc<CalendarEvent, CalendarState> {
-  CalendarBloc() : super(const CalendarInitial()) {
+  final JournalRepository _journalRepo;
+
+  CalendarBloc({required JournalRepository journalRepository})
+      : _journalRepo = journalRepository,
+        super(const CalendarInitial()) {
     on<CalendarMonthChanged>(_onMonthChanged);
     on<CalendarDaySelected>(_onDaySelected);
     on<CalendarViewModeChanged>(_onViewModeChanged);
-    on<CalendarLoadJournals>(_onLoadJournals);
   }
 
-  void _onMonthChanged(
+  Future<void> _onMonthChanged(
     CalendarMonthChanged event,
     Emitter<CalendarState> emit,
-  ) {
+  ) async {
     final currentState = state is CalendarLoaded ? state as CalendarLoaded : null;
 
     emit(CalendarLoaded(
@@ -123,9 +108,38 @@ class CalendarBloc extends Bloc<CalendarEvent, CalendarState> {
       journalsByDate: currentState?.journalsByDate ?? {},
       selectedDayJournals: [],
       viewMode: currentState?.viewMode ?? CalendarViewMode.month,
+      isLoading: true,
     ));
 
-    add(CalendarLoadJournals(event.month));
+    try {
+      // 加载当月日记
+      final startOfMonth = DateTime(event.month.year, event.month.month, 1);
+      final endOfMonth = DateTime(event.month.year, event.month.month + 1, 0);
+
+      final journals = await _journalRepo.getJournals(
+        dateFrom: startOfMonth,
+        dateTo: endOfMonth,
+      );
+
+      // 按日期索引
+      final byDate = <DateTime, List<JournalEntry>>{};
+      for (final journal in journals) {
+        final key = DateTime(journal.date.year, journal.date.month, journal.date.day);
+        byDate.putIfAbsent(key, () => []).add(journal);
+      }
+
+      if (state is CalendarLoaded) {
+        final current = state as CalendarLoaded;
+        emit(current.copyWith(
+          journalsByDate: byDate,
+          isLoading: false,
+        ));
+      }
+    } catch (e) {
+      if (state is CalendarLoaded) {
+        emit((state as CalendarLoaded).copyWith(isLoading: false));
+      }
+    }
   }
 
   void _onDaySelected(
@@ -135,7 +149,6 @@ class CalendarBloc extends Bloc<CalendarEvent, CalendarState> {
     if (state is! CalendarLoaded) return;
     final current = state as CalendarLoaded;
 
-    // 查找选中日期的日记
     final dayKey = DateTime(event.day.year, event.day.month, event.day.day);
     final dayJournals = current.journalsByDate[dayKey] ?? [];
 
@@ -150,26 +163,6 @@ class CalendarBloc extends Bloc<CalendarEvent, CalendarState> {
     Emitter<CalendarState> emit,
   ) {
     if (state is! CalendarLoaded) return;
-    final current = state as CalendarLoaded;
-    emit(current.copyWith(viewMode: event.mode));
-  }
-
-  Future<void> _onLoadJournals(
-    CalendarLoadJournals event,
-    Emitter<CalendarState> emit,
-  ) async {
-    if (state is! CalendarLoaded) return;
-    final current = state as CalendarLoaded;
-
-    emit(current.copyWith(isLoading: true));
-
-    // Phase 1: 使用空数据占位，待 Repository 集成后替换
-    // 实际将从 JournalRepository.loadByMonth(event.month) 获取
-    await Future.delayed(const Duration(milliseconds: 300));
-
-    emit(current.copyWith(
-      isLoading: false,
-      journalsByDate: current.journalsByDate,
-    ));
+    emit((state as CalendarLoaded).copyWith(viewMode: event.mode));
   }
 }