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/views/sticker_library_page.dart

@@ -1,26 +1,10 @@
-// 贴纸库页面 — 贴纸包浏览 + 贴纸网格
+// 贴纸库页面 — 贴纸包浏览 + 分类 Tab
 
 import 'package:flutter/material.dart';
+import 'package:flutter_bloc/flutter_bloc.dart';
 import 'package:nuanji_app/core/theme/app_colors.dart';
-
-/// 贴纸包数据模型
-class StickerPack {
-  final String id;
-  final String name;
-  final String? coverEmoji;
-  final int stickerCount;
-  final bool isFree;
-  final String? category;
-
-  const StickerPack({
-    required this.id,
-    required this.name,
-    this.coverEmoji,
-    this.stickerCount = 0,
-    this.isFree = true,
-    this.category,
-  });
-}
+import 'package:nuanji_app/data/remote/api_client.dart';
+import '../bloc/sticker_bloc.dart';
 
 /// 贴纸库页面 — 分类浏览贴纸包
 class StickerLibraryPage extends StatefulWidget {
@@ -30,93 +14,106 @@ class StickerLibraryPage extends StatefulWidget {
   State<StickerLibraryPage> createState() => _StickerLibraryPageState();
 }
 
-class _StickerLibraryPageState extends State<StickerLibraryPage>
-    with SingleTickerProviderStateMixin {
-  late TabController _tabController;
-
-  // Phase 1 占位数据
-  final _categories = ['全部', '动物', '食物', '自然', '节日', '表情'];
-
-  final _packs = const [
-    StickerPack(id: '1', name: '可爱猫咪', coverEmoji: '🐱', stickerCount: 24, isFree: true, category: '动物'),
-    StickerPack(id: '2', name: '小兔子系列', coverEmoji: '🐰', stickerCount: 20, isFree: true, category: '动物'),
-    StickerPack(id: '3', name: '甜品派对', coverEmoji: '🍰', stickerCount: 18, isFree: true, category: '食物'),
-    StickerPack(id: '4', name: '花朵合集', coverEmoji: '🌸', stickerCount: 22, isFree: true, category: '自然'),
-    StickerPack(id: '5', name: '夏日清凉', coverEmoji: '🍉', stickerCount: 16, isFree: true, category: '食物'),
-    StickerPack(id: '6', name: '星空物语', coverEmoji: '⭐', stickerCount: 20, isFree: false, category: '自然'),
-    StickerPack(id: '7', name: '开心表情', coverEmoji: '😄', stickerCount: 30, isFree: true, category: '表情'),
-    StickerPack(id: '8', name: '新年快乐', coverEmoji: '🎉', stickerCount: 15, isFree: false, category: '节日'),
-  ];
+class _StickerLibraryPageState extends State<StickerLibraryPage> {
+  late final StickerBloc _bloc;
 
   @override
   void initState() {
     super.initState();
-    _tabController = TabController(length: _categories.length, vsync: this);
+    _bloc = StickerBloc(api: context.read<ApiClient>());
+    _bloc.load();
   }
 
   @override
   void dispose() {
-    _tabController.dispose();
+    _bloc.dispose();
     super.dispose();
   }
 
   @override
   Widget build(BuildContext context) {
-    final theme = Theme.of(context);
-    final colorScheme = theme.colorScheme;
+    final colorScheme = Theme.of(context).colorScheme;
 
     return Scaffold(
-      appBar: AppBar(
-        title: const Text('贴纸库'),
-        bottom: TabBar(
-          controller: _tabController,
-          isScrollable: true,
-          tabAlignment: TabAlignment.start,
-          tabs: _categories.map((c) => Tab(text: c)).toList(),
-        ),
+      appBar: AppBar(title: const Text('贴纸库')),
+      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: 16),
+                  FilledButton.tonal(
+                    onPressed: _bloc.load,
+                    child: const Text('重试'),
+                  ),
+                ],
+              ),
+            );
+          }
+
+          final categories = state.categories;
+
+          return Column(
+            children: [
+              // 分类选择器（横向滚动 Chips）
+              SizedBox(
+                height: 48,
+                child: ListView(
+                  scrollDirection: Axis.horizontal,
+                  padding: const EdgeInsets.symmetric(horizontal: 16),
+                  children: categories.map((cat) {
+                    final isSelected = cat == state.selectedCategory;
+                    return Padding(
+                      padding: const EdgeInsets.only(right: 8),
+                      child: FilterChip(
+                        selected: isSelected,
+                        label: Text(cat),
+                        onSelected: (_) => _bloc.selectCategory(cat),
+                        selectedColor: colorScheme.primaryContainer,
+                        checkmarkColor: colorScheme.primary,
+                      ),
+                    );
+                  }).toList(),
+                ),
+              ),
+              const SizedBox(height: 8),
+
+              // 贴纸包网格
+              Expanded(
+                child: state.filteredPacks.isEmpty
+                    ? const Center(child: Text('暂无贴纸包'))
+                    : GridView.builder(
+                        padding: const EdgeInsets.all(16),
+                        gridDelegate:
+                            const SliverGridDelegateWithFixedCrossAxisCount(
+                          crossAxisCount: 2,
+                          mainAxisSpacing: 12,
+                          crossAxisSpacing: 12,
+                          childAspectRatio: 0.85,
+                        ),
+                        itemCount: state.filteredPacks.length,
+                        itemBuilder: (context, index) {
+                          return _StickerPackCard(
+                            pack: state.filteredPacks[index],
+                            colorScheme: colorScheme,
+                          );
+                        },
+                      ),
+              ),
+            ],
+          );
+        },
       ),
-      body: TabBarView(
-        controller: _tabController,
-        children: _categories.map((category) {
-          final filtered = category == '全部'
-              ? _packs
-              : _packs.where((p) => p.category == category).toList();
-          return _StickerPackGrid(packs: filtered, colorScheme: colorScheme);
-        }).toList(),
-      ),
-    );
-  }
-}
-
-/// 贴纸包网格
-class _StickerPackGrid extends StatelessWidget {
-  const _StickerPackGrid({
-    required this.packs,
-    required this.colorScheme,
-  });
-
-  final List<StickerPack> packs;
-  final ColorScheme colorScheme;
-
-  @override
-  Widget build(BuildContext context) {
-    if (packs.isEmpty) {
-      return const Center(child: Text('暂无贴纸包'));
-    }
-
-    return GridView.builder(
-      padding: const EdgeInsets.all(16),
-      gridDelegate: const SliverGridDelegateWithFixedCrossAxisCount(
-        crossAxisCount: 2,
-        mainAxisSpacing: 12,
-        crossAxisSpacing: 12,
-        childAspectRatio: 0.85,
-      ),
-      itemCount: packs.length,
-      itemBuilder: (context, index) {
-        final pack = packs[index];
-        return _StickerPackCard(pack: pack, colorScheme: colorScheme);
-      },
     );
   }
 }
@@ -143,7 +140,6 @@ class _StickerPackCard extends StatelessWidget {
       ),
       child: InkWell(
         onTap: () {
-          // Phase 1: 展示贴纸包详情页（待实现）
           ScaffoldMessenger.of(context).showSnackBar(
             SnackBar(content: Text('打开贴纸包: ${pack.name}')),
           );
@@ -164,7 +160,7 @@ class _StickerPackCard extends StatelessWidget {
                 ),
                 alignment: Alignment.center,
                 child: Text(
-                  pack.coverEmoji ?? '🎨',
+                  pack.coverImageUrl != null ? '🎨' : pack.displayCover,
                   style: const TextStyle(fontSize: 32),
                 ),
               ),
@@ -192,7 +188,8 @@ class _StickerPackCard extends StatelessWidget {
                   if (!pack.isFree) ...[
                     const SizedBox(width: 8),
                     Container(
-                      padding: const EdgeInsets.symmetric(horizontal: 6, vertical: 2),
+                      padding: const EdgeInsets.symmetric(
+                          horizontal: 6, vertical: 2),
                       decoration: BoxDecoration(
                         color: AppColors.accent.withValues(alpha: 0.15),
                         borderRadius: BorderRadius.circular(6),