Worker: interactive terminal WebSocket bridge (PTY in workspace container)

- attachTerminalServer() upgrades /jobs/:id/terminal WS connections, verifying a
  short-lived job-scoped HMAC token (verifyTerminalToken) so the browser never
  holds the worker secret
- Bridges the socket to a bash PTY via dockerode exec (Tty) in a persistent
  per-job shell container (spoon-agent-term-<id>) mounting the workspace; binary
  frames = stdin, JSON text frames = resize; idle containers reaped after 30m
- New env: SPOON_AGENT_TERMINAL_IMAGE/SECRET/IDLE_MS (secret falls back to the
  shared worker internal token)

turbo.json

@@ -37,6 +37,9 @@
     "SPOON_WORKER_TOKEN",
     "SPOON_AGENT_WORKER_ID",
     "SPOON_AGENT_JOB_IMAGE",
+    "SPOON_AGENT_TERMINAL_IMAGE",
+    "SPOON_AGENT_TERMINAL_SECRET",
+    "SPOON_AGENT_TERMINAL_IDLE_MS",
     "SPOON_AGENT_RUNTIME",
     "SPOON_AGENT_CONTAINER_RUNTIME",
     "SPOON_AGENT_CONTAINER_VOLUME_OPTIONS",