feat(booterm): add PTY session registry + listing endpoint

In-memory SessionMeta registry tracks active terminal sessions with
paneId, sessionId, projectPath, title, createdAt, lastActivityAt.
GET /api/term/sessions returns all active sessions as JSON array.
Registry is updated on WS attach and cleaned up on disconnect.

apps/booterm/src/ws/attach.ts

@@ -9,6 +9,7 @@ import {
 } from '../pty/manager.js';
 import { attachPty } from '../pty/pty.js';
 import { getUser } from '../auth.js';
+import { register, unregister } from '../pty/registry.js';
 
 export function registerWsAttachRoute(app: FastifyInstance, tmuxConfPath: string): void {
   app.get<{
@@ -57,6 +58,8 @@ export function registerWsAttachRoute(app: FastifyInstance, tmuxConfPath: string
         return;
       }
 
+      register(sid, pid, session.project_path);
+
       let handle: IPty;
       try {
         handle = attachPty({
@@ -157,6 +160,7 @@ export function registerWsAttachRoute(app: FastifyInstance, tmuxConfPath: string
       // teardown happens via the /kill route called from the frontend when the
       // user closes the pane.
       socket.on('close', () => {
+        unregister(pid);
         try {
           handle.kill();
         } catch {