feat(app): 设置页 UI + Mood/成就/贴纸 BLoC 接入 API + B7 测试扩展

前端改动:
- 新建设置页面 (主题切换/关于/隐私政策/用户协议/儿童隐私保护)
- SettingsBloc 注册到 MultiRepositoryProvider 全局可访问
- MoodBloc 修复编译错误 + 接入 /diary/stats/mood API
- MoodPage 添加错误状态展示和重试按钮
- AchievementBloc + 页面改造接入 /diary/achievements API
- StickerBloc + 页面改造接入 /diary/sticker-packs API
- TemplateBloc + 页面改造接入 /diary/templates API
- ProfilePage 设置入口改为跳转 /settings
- 添加 /settings 路由

后端改动:
- 扩展 mood_stats_service 测试 (连续天数算法/心情计数/边界场景)
- 新增 class_service 测试 (班级码生成/唯一性/错误映射)
- 新增 achievement_service 测试 (DTO 结构/序列化/map 构建)
- 新增 sticker_service 测试 (DTO 序列化/错误处理)
- 扩展 dto.rs 测试 (achievement/mood_stats/sticker/template/notification)
- 清理 2 个 unused import warning

验证:
- cargo check 0 error 0 warning
- flutter analyze 0 error

app/lib/features/mood/bloc/mood_bloc.dart

@@ -1,9 +1,10 @@
-// 心情 BLoC — 管理心情统计和趋势数据
+// 心情 BLoC — 通过 API 加载心情统计数据
 
 import 'package:flutter/material.dart';
 import 'package:nuanji_app/data/models/journal_entry.dart';
+import 'package:nuanji_app/data/remote/api_client.dart';
 
-// ===== 心情统计模型 =====
+// ===== 模型 =====
 
 /// 心情统计数据
 class MoodStats {
@@ -33,35 +34,20 @@ class MoodCount {
   });
 }
 
-/// 心情趋势数据点
-class MoodTrendPoint {
-  final DateTime date;
-  final Mood mood;
-  final int journalCount;
-
-  const MoodTrendPoint({
-    required this.date,
-    required this.mood,
-    required this.journalCount,
-  });
-}
-
 /// 统计周期
 enum StatsPeriod { week, month, quarter }
 
-// ===== 心情页面状态 =====
+// ===== State =====
 
 /// 心情页面状态
 class MoodState {
   final MoodStats stats;
-  final List<MoodTrendPoint> trendData;
   final StatsPeriod selectedPeriod;
   final bool isLoading;
   final String? errorMessage;
 
   const MoodState({
     this.stats = const MoodStats(),
-    this.trendData = const [],
     this.selectedPeriod = StatsPeriod.week,
     this.isLoading = false,
     this.errorMessage,
@@ -69,55 +55,27 @@ class MoodState {
 
   MoodState copyWith({
     MoodStats? stats,
-    List<MoodTrendPoint>? trendData,
     StatsPeriod? selectedPeriod,
     bool? isLoading,
     String? errorMessage,
   }) =>
       MoodState(
         stats: stats ?? this.stats,
-        trendData: trendData ?? this.trendData,
         selectedPeriod: selectedPeriod ?? this.selectedPeriod,
         isLoading: isLoading ?? this.isLoading,
         errorMessage: errorMessage,
       );
 }
 
-// ===== 心情 BLoC =====
+// ===== BLoC =====
 
+/// 心情统计 BLoC — ChangeNotifier 模式
 class MoodBloc extends ChangeNotifier {
+  final ApiClient _api;
   MoodState _state = const MoodState();
   MoodState get state => _state;
 
-  /// 切换统计周期
-  void changePeriod(StatsPeriod period) {
-    _state = _state.copyWith(selectedPeriod: period, isLoading: true);
-    notifyListeners();
-    _loadStats();
-  }
-
-  /// 加载统计数据
-  Future<void> _loadStats() async {
-    // Phase 1: 占位数据，待 API 集成后替换
-    await Future.delayed(const Duration(milliseconds: 300));
-
-    _state = _state.copyWith(
-      isLoading: false,
-      stats: MoodStats(
-        moodCounts: [
-          const MoodCount(mood: Mood.happy, count: 12, percentage: 40.0),
-          const MoodCount(mood: Mood.calm, count: 8, percentage: 26.7),
-          const MoodCount(mood: Mood.thinking, count: 5, percentage: 16.7),
-          const MoodCount(mood: Mood.sad, count: 3, percentage: 10.0),
-          const MoodCount(mood: Mood.angry, count: 2, percentage: 6.6),
-        ],
-        streakDays: 7,
-        totalJournals: 30,
-        dominantMood: Mood.happy,
-      ),
-    );
-    notifyListeners();
-  }
+  MoodBloc({required ApiClient api}) : _api = api;
 
   /// 初始加载
   void load() {
@@ -125,4 +83,66 @@ class MoodBloc extends ChangeNotifier {
     notifyListeners();
     _loadStats();
   }
+
+  /// 切换统计周期
+  void changePeriod(StatsPeriod period) {
+    if (period == _state.selectedPeriod) return;
+    _state = _state.copyWith(selectedPeriod: period, isLoading: true);
+    notifyListeners();
+    _loadStats();
+  }
+
+  Future<void> _loadStats() async {
+    try {
+      final periodStr = switch (_state.selectedPeriod) {
+        StatsPeriod.week => 'week',
+        StatsPeriod.month => 'month',
+        StatsPeriod.quarter => 'quarter',
+      };
+
+      final response = await _api.get(
+        '/diary/stats/mood',
+        queryParams: {'period': periodStr},
+      );
+      final body = response.data as Map<String, dynamic>;
+      final data = body['data'] as Map<String, dynamic>;
+
+      final counts = (data['mood_counts'] as List? ?? [])
+          .map((item) {
+            final m = item as Map<String, dynamic>;
+            return MoodCount(
+              mood: Mood.values.firstWhere(
+                (v) => v.value == m['mood'],
+                orElse: () => Mood.happy,
+              ),
+              count: (m['count'] as num).toInt(),
+              percentage: (m['percentage'] as num).toDouble(),
+            );
+          })
+          .toList();
+
+      final dominant = data['dominant_mood'] != null
+          ? Mood.values.firstWhere(
+              (v) => v.value == data['dominant_mood'],
+              orElse: () => Mood.happy,
+            )
+          : null;
+
+      _state = _state.copyWith(
+        isLoading: false,
+        stats: MoodStats(
+          moodCounts: counts,
+          streakDays: (data['streak_days'] as num?)?.toInt() ?? 0,
+          totalJournals: (data['total_journals'] as num?)?.toInt() ?? 0,
+          dominantMood: dominant,
+        ),
+      );
+    } catch (e) {
+      _state = _state.copyWith(
+        isLoading: false,
+        errorMessage: '加载统计数据失败',
+      );
+    }
+    notifyListeners();
+  }
 }