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/routes/sessions.ts

@@ -0,0 +1,18 @@
+import type { FastifyInstance } from 'fastify';
+import { list } from '../pty/registry.js';
+
+export function registerSessionRoutes(app: FastifyInstance): void {
+  app.get('/api/term/sessions', async (_req, reply) => {
+    const active = list();
+    return reply.code(200).send({
+      sessions: active.map((s) => ({
+        paneId: s.paneId,
+        sessionId: s.sessionId,
+        projectPath: s.projectPath,
+        title: s.title ?? null,
+        createdAt: s.createdAt.toISOString(),
+        lastActivityAt: s.lastActivityAt.toISOString(),
+      })),
+    });
+  });
+}