feat(ai-proxy): Update 9router button — shut down, npm update, relaunch hidden

Settings → AI Proxy gains an admin-only Update 9router button beside
Config 9router. One in-memory job (server/lib/nine-router-update.js) stops
9router (its user unit, else this account's own 9router processes), runs
npm install -g --prefix <its prefix> 9router@latest (sudo -n only when
sudoers already allows it, probed before anything stops), then relaunches
it hidden only if it was running. A failed update still relaunches the old
version. Nothing in the request names a command, path or package.

client/src/pages/AiProxyConfig.tsx

@@ -30,6 +30,8 @@
  * — on the DASHBOARD's host at `NINE_ROUTER_PORT` (`nineRouterUrl`), never the
  * viewer's own localhost: a teammate on the LAN has no 9router of their own.
  * It is shown only when the server finds a `9router` binary installed.
+ * Beside it an admin gets **Update 9router** (`NineRouterUpdate`): shut it
+ * down, `npm install -g 9router@latest`, start it again hidden.
  *
  * **Test** asks the endpoint itself, once as Claude Code would
  * (`/v1/messages`) and once as Codex would (`/v1/responses`), one line each.
@@ -54,6 +56,7 @@ import { confirmDialog } from "../lib/confirm";
 import { copyText } from "../lib/clipboard";
 import { useDialog } from "../hooks/useDialog";
 import { useAuth } from "../components/AuthGate";
+import { NineRouterUpdate } from "../components/settings/NineRouterUpdate";
 
 const NINE_ROUTER_PORT = 20128;
 
@@ -271,6 +274,7 @@ export function AiProxyConfig() {
               {t("aiProxy.config9router")}
             </a>
           )}
+          {nineRouter && isAdmin && <NineRouterUpdate />}
           <button
             type="button"
             onClick={startAdd}