feat(admin): add model config CRUD and platform bridge pages

- Backend: ModelConfigStore with Provider/Model/Routing CRUD
- Backend: /api/v1/admin/models/config endpoints
- Frontend: ModelsPage with 3-tab editor (providers/models/routing)
- Frontend: BridgePage showing adapter status + group chat rules
- Admin nav expanded to 9 items

frontend/web/src/components/admin/AdminLayout.tsx

@@ -4,8 +4,10 @@ const navItems = [
   { to: '/admin/dashboard', label: '仪表盘', icon: '◉' },
   { to: '/admin/services', label: '服务管理', icon: '⚙' },
   { to: '/admin/iot', label: 'IoT 设备', icon: '⌂' },
+  { to: '/admin/models', label: '模型配置', icon: '◆' },
   { to: '/admin/plugins', label: '插件管理', icon: '◇' },
   { to: '/admin/memory', label: '记忆管理', icon: '♡' },
+  { to: '/admin/bridge', label: '平台桥接', icon: '↗' },
   { to: '/admin/llm-calls', label: 'LLM 日志', icon: '🧠' },
   { to: '/admin/system', label: '系统信息', icon: '⊞' },
 ]