refactor: 拆分 middleware/router 为单一职责文件，新增站点设置管理页面

middleware:
- 拆分 auth.go → auth.go + auth_token.go + auth_parser.go + auth_admin.go
- 拆分 csrf.go → csrf.go + csrf_token.go
- 拆分 ratelimit.go → ratelimit.go + ratelimit_core.go + ratelimit_cleanup.go
- 修复 import 未使用/缺失问题

router:
- 拆分 router.go → admin.go + api.go + frontend.go + deps_core.go + deps_extra.go

feat(admin): 站点设置管理页面
- 新增 SSR 页面 /admin/site-settings（仅 Owner）
- 审核开关 Toggle 即时保存
- 通用设置展示
- 侧边栏新增站点设置入口
- 注册 UpdateBoolSetting/GetBoolSetting API 路由

templates/admin/html/site-settings/index.html

@@ -0,0 +1,64 @@
+{{template "admin/layout/base.html" .}}
+        <div class="page-header">
+            <h1>站点设置</h1>
+            <p class="page-desc">管理审核开关与站点全局配置</p>
+        </div>
+
+        <!-- 审核设置 -->
+        <div class="settings-section">
+            <div class="section-title">审核设置</div>
+            <div class="section-body">
+                <div class="setting-item">
+                    <div class="setting-info">
+                        <span class="setting-label">启用审核系统</span>
+                        <span class="setting-desc">启用后，用户名、头像、签名修改将进入审核流程</span>
+                    </div>
+                    <label class="toggle-switch">
+                        <input type="checkbox" id="audit-enabled" data-key="audit.enabled">
+                        <span class="toggle-slider"></span>
+                    </label>
+                </div>
+
+                <div class="setting-item">
+                    <div class="setting-info">
+                        <span class="setting-label">用户名审核</span>
+                        <span class="setting-desc">更改用户名需要管理员审核</span>
+                    </div>
+                    <label class="toggle-switch">
+                        <input type="checkbox" id="audit-username" data-key="audit.username_audit">
+                        <span class="toggle-slider"></span>
+                    </label>
+                </div>
+
+                <div class="setting-item">
+                    <div class="setting-info">
+                        <span class="setting-label">头像审核</span>
+                        <span class="setting-desc">更改头像需要管理员审核</span>
+                    </div>
+                    <label class="toggle-switch">
+                        <input type="checkbox" id="audit-avatar" data-key="audit.avatar_audit">
+                        <span class="toggle-slider"></span>
+                    </label>
+                </div>
+
+                <div class="setting-item">
+                    <div class="setting-info">
+                        <span class="setting-label">签名审核</span>
+                        <span class="setting-desc">更改个人签名需要管理员审核</span>
+                    </div>
+                    <label class="toggle-switch">
+                        <input type="checkbox" id="audit-bio" data-key="audit.bio_audit">
+                        <span class="toggle-slider"></span>
+                    </label>
+                </div>
+            </div>
+        </div>
+
+        <!-- 通用设置 -->
+        <div class="settings-section">
+            <div class="section-title">通用设置</div>
+            <div class="section-body" id="general-settings">
+                <div class="settings-empty" id="settings-empty">加载中...</div>
+            </div>
+        </div>
+{{template "admin/layout/footer.html" .}}