API: implement /containers/{id}/wait (blocking exit-code endpoint)

[adrianlungu]

Long-poll endpoint that blocks until the container exits and returns the exit code as JSON.

Surfaced by

• `docker run -d` reports `error waiting for container: Error response from daemon: 404 page not found` even when the container starts successfully — the CLI always calls /wait after start
• `docker wait ` fails outright
• Testcontainers and most orchestration tooling call this after creating a container

What it needs

`POST /containers/{id}/wait` with optional `condition` query param:

• `not-running` (default) — container is not running (exited)
• `next-exit` — wait for exit after the current run
• `removed` — waits until the container is removed

Response shape:

```json
{
"StatusCode": 0,
"Error": null
}
```

Scope

Small compared to /attach — single long-poll, no stream framing, no stdin. Just:

1. Subscribe to `container.die` / `container.stop` events on the existing bus
2. Block until the matching event arrives for the given ID
3. Emit StatusCode from the container's exit code (need to start tracking this — currently only /exec/{id}/json does)
4. Honor ctx cancellation cleanly

Bucket this with /attach implementation since they share "track container exit code" plumbing.