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/stickers/bloc/sticker_bloc.dart

@@ -0,0 +1,181 @@
+// 贴纸 BLoC — 通过 API 加载贴纸包和贴纸数据
+
+import 'package:flutter/material.dart';
+import 'package:nuanji_app/data/remote/api_client.dart';
+
+// ===== 模型 =====
+
+/// 贴纸包
+class StickerPack {
+  final String id;
+  final String name;
+  final String? description;
+  final String? coverImageUrl;
+  final int stickerCount;
+  final bool isFree;
+  final String? category;
+
+  const StickerPack({
+    required this.id,
+    required this.name,
+    this.description,
+    this.coverImageUrl,
+    this.stickerCount = 0,
+    this.isFree = true,
+    this.category,
+  });
+
+  /// 兼容旧 UI 的 emoji 封面（优先用 coverImageUrl，否则用默认）
+  String get displayCover => coverImageUrl ?? '🎨';
+}
+
+/// 单张贴纸
+class Sticker {
+  final String id;
+  final String packId;
+  final String name;
+  final String imageUrl;
+  final String? category;
+
+  const Sticker({
+    required this.id,
+    required this.packId,
+    required this.name,
+    required this.imageUrl,
+    this.category,
+  });
+}
+
+// ===== State =====
+
+/// 贴纸页面状态
+class StickerState {
+  final List<StickerPack> packs;
+  final String selectedCategory;
+  final bool isLoading;
+  final String? errorMessage;
+
+  const StickerState({
+    this.packs = const [],
+    this.selectedCategory = '全部',
+    this.isLoading = false,
+    this.errorMessage,
+  });
+
+  /// 按分类过滤贴纸包
+  List<StickerPack> get filteredPacks => selectedCategory == '全部'
+      ? packs
+      : packs.where((p) => p.category == selectedCategory).toList();
+
+  /// 所有分类（去重 + 加"全部"）
+  List<String> get categories {
+    final cats = packs
+        .map((p) => p.category)
+        .whereType<String>()
+        .toSet()
+        .toList();
+    return ['全部', ...cats];
+  }
+
+  StickerState copyWith({
+    List<StickerPack>? packs,
+    String? selectedCategory,
+    bool? isLoading,
+    String? errorMessage,
+  }) =>
+      StickerState(
+        packs: packs ?? this.packs,
+        selectedCategory: selectedCategory ?? this.selectedCategory,
+        isLoading: isLoading ?? this.isLoading,
+        errorMessage: errorMessage,
+      );
+}
+
+// ===== BLoC =====
+
+/// 贴纸 BLoC — ChangeNotifier 模式
+class StickerBloc extends ChangeNotifier {
+  final ApiClient _api;
+  StickerState _state = const StickerState();
+  StickerState get state => _state;
+
+  StickerBloc({required ApiClient api}) : _api = api;
+
+  /// 加载贴纸包列表
+  void load() {
+    _state = _state.copyWith(isLoading: true);
+    notifyListeners();
+    _fetchPacks();
+  }
+
+  /// 选择分类
+  void selectCategory(String category) {
+    _state = _state.copyWith(selectedCategory: category);
+    notifyListeners();
+  }
+
+  /// 按分类加载贴纸包
+  void loadByCategory(String? category) {
+    _state = _state.copyWith(isLoading: true);
+    notifyListeners();
+    _fetchPacks(category: category);
+  }
+
+  Future<void> _fetchPacks({String? category}) async {
+    try {
+      final queryParams = category != null && category != '全部'
+          ? {'category': category}
+          : null;
+
+      final response = await _api.get(
+        '/diary/sticker-packs',
+        queryParams: queryParams,
+      );
+      final body = response.data as Map<String, dynamic>;
+      final list = body['data'] as List? ?? [];
+
+      final packs = list.map((item) {
+        final m = item as Map<String, dynamic>;
+        return StickerPack(
+          id: m['id'] as String,
+          name: m['name'] as String,
+          description: m['description'] as String?,
+          coverImageUrl: m['cover_image_url'] as String?,
+          stickerCount: (m['sticker_count'] as num?)?.toInt() ?? 0,
+          isFree: m['is_free'] as bool? ?? true,
+          category: m['category'] as String?,
+        );
+      }).toList();
+
+      _state = _state.copyWith(isLoading: false, packs: packs);
+    } catch (e) {
+      _state = _state.copyWith(
+        isLoading: false,
+        errorMessage: '加载贴纸包失败',
+      );
+    }
+    notifyListeners();
+  }
+
+  /// 获取贴纸包内的贴纸列表
+  Future<List<Sticker>> fetchStickersInPack(String packId) async {
+    try {
+      final response = await _api.get('/diary/sticker-packs/$packId/stickers');
+      final body = response.data as Map<String, dynamic>;
+      final list = body['data'] as List? ?? [];
+
+      return list.map((item) {
+        final m = item as Map<String, dynamic>;
+        return Sticker(
+          id: m['id'] as String,
+          packId: m['pack_id'] as String,
+          name: m['name'] as String,
+          imageUrl: m['image_url'] as String,
+          category: m['category'] as String?,
+        );
+      }).toList();
+    } catch (e) {
+      return [];
+    }
+  }
+}