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-lock.json

@@ -12,6 +12,7 @@
         "next": "^16.0.0",
         "react": "^19.0.0",
         "react-dom": "^19.0.0",
+        "react-easy-crop": "^6.2.3",
         "react-markdown": "^9.0.1"
       },
       "devDependencies": {
@@ -2509,6 +2510,12 @@
         "node": "^10 || ^12 || >=14"
       }
     },
+    "node_modules/normalize-wheel": {
+      "version": "1.0.1",
+      "resolved": "https://registry.npmjs.org/normalize-wheel/-/normalize-wheel-1.0.1.tgz",
+      "integrity": "sha512-1OnlAPZ3zgrk8B91HyRj+eVv+kS5u+Z0SCsak6Xil/kmgEia50ga7zfkumayonZrImffAxPU/5WcyGhzetHNPA==",
+      "license": "BSD-3-Clause"
+    },
     "node_modules/parse-entities": {
       "version": "4.0.2",
       "resolved": "https://registry.npmjs.org/parse-entities/-/parse-entities-4.0.2.tgz",
@@ -2600,6 +2607,19 @@
         "react": "^19.3.0"
       }
     },
+    "node_modules/react-easy-crop": {
+      "version": "6.2.3",
+      "resolved": "https://registry.npmjs.org/react-easy-crop/-/react-easy-crop-6.2.3.tgz",
+      "integrity": "sha512-ebimG3OGlzizjxEZ77Cj9CVLcg5vDZ6QVz8ud1rx4WmsCDWHIROEhgMi0GpJ/jKAuwHrH0M+QZUK4hyvxbYhOA==",
+      "license": "MIT",
+      "dependencies": {
+        "normalize-wheel": "^1.0.1"
+      },
+      "peerDependencies": {
+        "react": ">=16.4.0",
+        "react-dom": ">=16.4.0"
+      }
+    },
     "node_modules/react-markdown": {
       "version": "9.1.0",
       "resolved": "https://registry.npmjs.org/react-markdown/-/react-markdown-9.1.0.tgz",