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/achievement/bloc/achievement_bloc.dart

@@ -0,0 +1,108 @@
+// 成就 BLoC — 通过 API 加载成就列表
+
+import 'package:flutter/material.dart';
+import 'package:nuanji_app/data/remote/api_client.dart';
+
+// ===== 模型 =====
+
+/// 成就数据
+class Achievement {
+  final String id;
+  final String code;
+  final String name;
+  final String? description;
+  final String? icon;
+  final String category;
+  final bool isUnlocked;
+  final DateTime? unlockedAt;
+
+  const Achievement({
+    required this.id,
+    required this.code,
+    required this.name,
+    this.description,
+    this.icon,
+    required this.category,
+    this.isUnlocked = false,
+    this.unlockedAt,
+  });
+}
+
+// ===== State =====
+
+/// 成就页面状态
+class AchievementState {
+  final List<Achievement> achievements;
+  final bool isLoading;
+  final String? errorMessage;
+
+  const AchievementState({
+    this.achievements = const [],
+    this.isLoading = false,
+    this.errorMessage,
+  });
+
+  int get unlockedCount =>
+      achievements.where((a) => a.isUnlocked).length;
+
+  AchievementState copyWith({
+    List<Achievement>? achievements,
+    bool? isLoading,
+    String? errorMessage,
+  }) =>
+      AchievementState(
+        achievements: achievements ?? this.achievements,
+        isLoading: isLoading ?? this.isLoading,
+        errorMessage: errorMessage,
+      );
+}
+
+// ===== BLoC =====
+
+/// 成就 BLoC — ChangeNotifier 模式
+class AchievementBloc extends ChangeNotifier {
+  final ApiClient _api;
+  AchievementState _state = const AchievementState();
+  AchievementState get state => _state;
+
+  AchievementBloc({required ApiClient api}) : _api = api;
+
+  /// 加载成就列表
+  void load() {
+    _state = _state.copyWith(isLoading: true);
+    notifyListeners();
+    _fetchAchievements();
+  }
+
+  Future<void> _fetchAchievements() async {
+    try {
+      final response = await _api.get('/diary/achievements');
+      final body = response.data as Map<String, dynamic>;
+      final list = body['data'] as List? ?? [];
+
+      final achievements = list.map((item) {
+        final m = item as Map<String, dynamic>;
+        return Achievement(
+          id: m['id'] as String,
+          code: m['code'] as String,
+          name: m['name'] as String,
+          description: m['description'] as String?,
+          icon: m['icon'] as String?,
+          category: m['category'] as String,
+          isUnlocked: m['is_unlocked'] as bool? ?? false,
+          unlockedAt: m['unlocked_at'] != null
+              ? DateTime.tryParse(m['unlocked_at'] as String)
+              : null,
+        );
+      }).toList();
+
+      _state = _state.copyWith(isLoading: false, achievements: achievements);
+    } catch (e) {
+      _state = _state.copyWith(
+        isLoading: false,
+        errorMessage: '加载成就列表失败',
+      );
+    }
+    notifyListeners();
+  }
+}

app/lib/features/achievement/views/achievement_page.dart

@@ -1,92 +1,109 @@
 // 成就页面 — 徽章收集展示
 
 import 'package:flutter/material.dart';
+import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:nuanji_app/core/theme/app_colors.dart';
-
-/// 成就数据模型
-class Achievement {
-  final String id;
-  final String code;
-  final String name;
-  final String? description;
-  final String icon;
-  final String category;
-  final bool isUnlocked;
-
-  const Achievement({
-    required this.id,
-    required this.code,
-    required this.name,
-    this.description,
-    required this.icon,
-    required this.category,
-    this.isUnlocked = false,
-  });
-}
+import 'package:nuanji_app/data/remote/api_client.dart';
+import '../bloc/achievement_bloc.dart';
 
 /// 成就页面 — 徽章收集和展示
-class AchievementPage extends StatelessWidget {
+class AchievementPage extends StatefulWidget {
   const AchievementPage({super.key});
 
-  static const _achievements = [
-    Achievement(id: '1', code: 'first_diary', name: '初次落笔', description: '写下第一篇日记', icon: '✏️', category: 'writing', isUnlocked: true),
-    Achievement(id: '2', code: 'streak_7', name: '坚持一周', description: '连续写日记 7 天', icon: '🔥', category: 'writing'),
-    Achievement(id: '3', code: 'streak_30', name: '月度达人', description: '连续写日记 30 天', icon: '💪', category: 'writing'),
-    Achievement(id: '4', code: 'sticker_collector', name: '贴纸收藏家', description: '收集 10 张贴纸', icon: '🎨', category: 'collection'),
-    Achievement(id: '5', code: 'social_butterfly', name: '分享之星', description: '分享 5 篇日记到班级', icon: '🌟', category: 'social'),
-    Achievement(id: '6', code: 'mood_tracker', name: '心情记录员', description: '连续记录心情 14 天', icon: '🌈', category: 'writing'),
-    Achievement(id: '7', code: 'early_bird', name: '早起日记', description: '在早上 7 点前写日记', icon: '🌅', category: 'special'),
-    Achievement(id: '8', code: 'artist', name: '小画家', description: '在日记中画 10 幅涂鸦', icon: '🖌️', category: 'collection'),
-  ];
+  @override
+  State<AchievementPage> createState() => _AchievementPageState();
+}
+
+class _AchievementPageState extends State<AchievementPage> {
+  late final AchievementBloc _bloc;
+
+  @override
+  void initState() {
+    super.initState();
+    _bloc = AchievementBloc(api: context.read<ApiClient>());
+    _bloc.load();
+  }
+
+  @override
+  void dispose() {
+    _bloc.dispose();
+    super.dispose();
+  }
 
   @override
   Widget build(BuildContext context) {
     final theme = Theme.of(context);
     final colorScheme = theme.colorScheme;
-    final unlocked = _achievements.where((a) => a.isUnlocked).length;
 
     return Scaffold(
-      appBar: AppBar(
-        title: const Text('成就'),
-      ),
-      body: SingleChildScrollView(
-        padding: const EdgeInsets.all(16),
-        child: Column(
-          crossAxisAlignment: CrossAxisAlignment.start,
-          children: [
-            // 进度概览
-            _AchievementProgressCard(
-              unlocked: unlocked,
-              total: _achievements.length,
-              colorScheme: colorScheme,
-            ),
-            const SizedBox(height: 24),
-            Text(
-              '全部成就',
-              style: theme.textTheme.titleMedium?.copyWith(
-                fontWeight: FontWeight.bold,
+      appBar: AppBar(title: const Text('成就')),
+      body: ListenableBuilder(
+        listenable: _bloc,
+        builder: (context, _) {
+          final state = _bloc.state;
+
+          if (state.isLoading) {
+            return const Center(child: CircularProgressIndicator());
+          }
+
+          if (state.errorMessage != null) {
+            return Center(
+              child: Column(
+                mainAxisAlignment: MainAxisAlignment.center,
+                children: [
+                  Icon(Icons.error_outline, size: 48, color: colorScheme.error),
+                  const SizedBox(height: 12),
+                  Text(state.errorMessage!, style: theme.textTheme.bodyMedium),
+                  const SizedBox(height: 16),
+                  FilledButton.tonal(
+                    onPressed: _bloc.load,
+                    child: const Text('重试'),
+                  ),
+                ],
               ),
-            ),
-            const SizedBox(height: 12),
-            GridView.builder(
-              shrinkWrap: true,
-              physics: const NeverScrollableScrollPhysics(),
-              gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
-                crossAxisCount: 2,
-                mainAxisSpacing: 12,
-                crossAxisSpacing: 12,
-                childAspectRatio: 0.75,
-              ),
-              itemCount: _achievements.length,
-              itemBuilder: (context, index) {
-                return _AchievementCard(
-                  achievement: _achievements[index],
+            );
+          }
+
+          return SingleChildScrollView(
+            padding: const EdgeInsets.all(16),
+            child: Column(
+              crossAxisAlignment: CrossAxisAlignment.start,
+              children: [
+                // 进度概览
+                _AchievementProgressCard(
+                  unlocked: state.unlockedCount,
+                  total: state.achievements.length,
                   colorScheme: colorScheme,
-                );
-              },
+                ),
+                const SizedBox(height: 24),
+                Text(
+                  '全部成就',
+                  style: theme.textTheme.titleMedium?.copyWith(
+                    fontWeight: FontWeight.bold,
+                  ),
+                ),
+                const SizedBox(height: 12),
+                GridView.builder(
+                  shrinkWrap: true,
+                  physics: const NeverScrollableScrollPhysics(),
+                  gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
+                    crossAxisCount: 2,
+                    mainAxisSpacing: 12,
+                    crossAxisSpacing: 12,
+                    childAspectRatio: 0.75,
+                  ),
+                  itemCount: state.achievements.length,
+                  itemBuilder: (context, index) {
+                    return _AchievementCard(
+                      achievement: state.achievements[index],
+                      colorScheme: colorScheme,
+                    );
+                  },
+                ),
+              ],
             ),
-          ],
-        ),
+          );
+        },
       ),
     );
   }
@@ -194,7 +211,10 @@ class _AchievementCard extends StatelessWidget {
               ),
               alignment: Alignment.center,
               child: achievement.isUnlocked
-                  ? Text(achievement.icon, style: const TextStyle(fontSize: 28))
+                  ? Text(
+                      achievement.icon ?? '🏆',
+                      style: const TextStyle(fontSize: 28),
+                    )
                   : Icon(
                       Icons.lock_outline,
                       color: colorScheme.onSurface.withValues(alpha: 0.3),