fix(terminal): reconcile tabs with server sessions and keep shown terminals alive

The tab list lived only in per-tab sessionStorage, so a new browser
tab, another device, or cleared storage showed an empty terminal
sidebar while PTYs kept running server-side, and orphans leaked until
the idle sweep. Add GET /api/terminal/sessions and adopt unknown
server sessions into the local tab projection (additive only; a failed
listing changes nothing).

The idle sweep also reaped terminals in background tabs because only
the active tab holds a WebSocket attachment. Add POST
/api/terminal/touch and have open clients periodically refresh
activity for every session their tabs reference.

packages/web/src/api/terminal.ts

@@ -8,6 +8,8 @@ import {
   restartTerminalSession,
   forceKillTerminal,
   listTerminalShells,
+  listTerminalSessions,
+  touchTerminalSessions,
 } from '@openchamber/ui/lib/terminalApi';
 import type {
   TerminalAPI,
@@ -23,6 +25,14 @@ export const createWebTerminalAPI = (): TerminalAPI => ({
     return listTerminalShells();
   },
 
+  async listSessions(cwd: string) {
+    return listTerminalSessions(cwd);
+  },
+
+  async touchSessions(sessionIds: string[]) {
+    await touchTerminalSessions(sessionIds);
+  },
+
   async createSession(options: CreateTerminalOptions): Promise<TerminalSession> {
     return createTerminalSession(options);
   },