Two web spawn QoL improvements plus the wire support they need:
- Command field now prefills `claude` instead of an empty box.
- Working directory prefills the selected daemon's home dir, updating on
daemon change unless the user has typed their own value.
The daemon resolves its `$HOME` via `dirs::home_dir()` at startup and
advertises it end-to-end: a new `home_dir` field on `DaemonOutbound::Hello`
flows through the registry's `register` into `DaemonInfo` (served on
`/api/daemons` and `/api/events`). The field is `#[serde(default)]`, so older
daemons that omit it deserialize to an empty string — backward compatible, and
the UI simply skips prefill when it's empty.
Hierarchical `/`-separated labels in the web sidebar already worked
(web/src/catalog.ts); no change there.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>