feat: 功能清单进智能体提示，补字幕按功能模块约定改为样板

- 外围功能模块(补字幕、原站视图、桌面模式、网页搜索、MCP、定时任务)声明 manifest,与 FEATURES 一一对应;
  系统提示「能力地图」末尾列出外围功能(没有开关,能力只列本次可用的)
- 补字幕:订阅 organization.finished(认出值得补字幕的整理,自动补字幕还没做,不建任务),
  写入字幕后在同一事务发 subtitle.written;原有行为不变

Co-Authored-By: Claude Opus 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01Cxwgnn2pbzQ7rXv3rq7fei

apps/server/src/modules/websearch/index.ts

@@ -1,3 +1,4 @@
+import { featureManifest } from "@umt/contracts";
 import type { ServerContext, ServerModule } from "../types.ts";
 import { registerWebSearchCapabilities } from "./capabilities.ts";
 import { registerWebSearchRoutes } from "./routes.ts";
@@ -24,6 +25,7 @@ export function createWebSearchModule(opts: WebSearchModuleOptions = {}): Server
   };
   return {
     name: "websearch",
+    manifest: featureManifest("websearch"),
     service,
     registerRoutes(app, ctx) {
       registerWebSearchRoutes(app, () => service(ctx));