feat: 完成头像上传、站点主题配置与UI优化

- 新增附件模型与上传服务，拆分头像上传/管理逻辑
- 重构用户资料接口，移除直接修改头像字段，改用专用上传接口
- 添加站点公开设置API与管理员外观配置页
- 全局替换hover背景为accent-soft，优化交互一致性
- 完善头像组件，支持图片加载失败回退与src更新重置
- 新增用户状态事件总线，解决同页头像更新不及时问题
- 调整依赖包顺序与CI依赖版本
- 重构板块列表接口，新增帖子计数
- 迁移账号设置到用户主页tab，合并重复代码

frontend/package.json

@@ -9,18 +9,19 @@
     "lint": "next lint"
   },
   "dependencies": {
+    "lucide-react": "^0.460.0",
     "next": "^16.0.0",
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
-    "lucide-react": "^0.460.0",
+    "react-easy-crop": "^6.2.3",
     "react-markdown": "^9.0.1"
   },
   "devDependencies": {
+    "@tailwindcss/postcss": "^4.0.0",
     "@types/node": "^22.0.0",
     "@types/react": "^19.0.0",
     "@types/react-dom": "^19.0.0",
     "tailwindcss": "^4.0.0",
-    "@tailwindcss/postcss": "^4.0.0",
     "typescript": "^5.7.0"
   }
 }