feat(maestro): spawn form defaults command to claude + prefills cwd to daemon home dir (NAP-328)

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>

crates/maestro-daemon/tests/local_api.rs

@@ -117,6 +117,7 @@ async fn list_daemons_includes_self_and_mirrored_peers() {
                 hostname: "konishi-host".into(),
                 version: "0.1.0".into(),
                 daemon_url: "ws://10.0.0.2:7070".into(),
+                home_dir: String::new(),
             },
         })
         .await;