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-protocol/src/lib.rs

@@ -100,6 +100,11 @@ pub enum DaemonOutbound {
         /// in `GET /api/sessions/:id/connect-info` so the client can connect
         /// directly. Example: `ws://10.0.0.1:8081`.
         daemon_url: String,
+        /// Absolute home directory of the OS user this daemon runs as, used by
+        /// clients to prefill a spawn form's working directory. Empty when the
+        /// daemon could not resolve `$HOME`. (NAP-328)
+        #[serde(default)]
+        home_dir: String,
     },
     SessionsSnapshot {
         sessions: Vec<Session>,
@@ -234,6 +239,11 @@ pub struct DaemonInfo {
     pub hostname: String,
     pub version: String,
     pub daemon_url: String,
+    /// Absolute home directory of the OS user the daemon runs as. Clients use
+    /// it to prefill the spawn form's working directory. Empty when unknown
+    /// (older daemon, or `$HOME` unresolved). (NAP-328)
+    #[serde(default)]
+    pub home_dir: String,
 }
 
 /// Response body for `GET /api/sessions/:id/connect-info`.
@@ -528,6 +538,7 @@ mod tests {
             version: PROTOCOL_VERSION.into(),
             token: "shhh".into(),
             daemon_url: "ws://10.0.0.1:8081".into(),
+            home_dir: String::new(),
         };
         let v = serde_json::to_value(&hello).unwrap();
         assert_eq!(v["type"], "Hello");
@@ -656,10 +667,25 @@ mod tests {
             hostname: "naps-laptop".into(),
             version: "0.1.0".into(),
             daemon_url: "ws://10.0.0.1:8081".into(),
+            home_dir: "/home/naps62".into(),
         };
         assert_eq!(d, round_trip(&d));
     }
 
+    #[test]
+    fn daemon_info_home_dir_defaults_when_absent() {
+        // Older daemons / pre-NAP-328 payloads omit `home_dir`; it must
+        // deserialize to an empty string rather than failing.
+        let json = r#"{
+            "daemon_id": "laptop",
+            "hostname": "naps-laptop",
+            "version": "0.1.0",
+            "daemon_url": "ws://10.0.0.1:8081"
+        }"#;
+        let d: DaemonInfo = serde_json::from_str(json).unwrap();
+        assert_eq!(d.home_dir, "");
+    }
+
     #[test]
     fn connect_info_round_trips() {
         let c = ConnectInfo {
@@ -676,6 +702,7 @@ mod tests {
             hostname: "naps-laptop".into(),
             version: "0.1.0".into(),
             daemon_url: "ws://10.0.0.1:8081".into(),
+            home_dir: String::new(),
         };
         let session = sample_session();
         let variants = vec![
@@ -882,12 +909,14 @@ mod tests {
                     hostname: "naps-laptop".into(),
                     version: "0.1.0".into(),
                     daemon_url: "ws://10.0.0.1:7070".into(),
+                    home_dir: String::new(),
                 },
                 DaemonInfo {
                     daemon_id: "konishi".into(),
                     hostname: "konishi".into(),
                     version: "0.1.0".into(),
                     daemon_url: "ws://10.0.0.2:7070".into(),
+                    home_dir: String::new(),
                 },
             ],
             sessions: vec![mine.clone(), peer_session.clone()],
@@ -929,6 +958,7 @@ mod tests {
                 hostname: "x".into(),
                 version: "y".into(),
                 daemon_url: "z".into(),
+                home_dir: String::new(),
             }
         }
         .for_peer("laptop")
@@ -966,6 +996,7 @@ mod tests {
                     hostname: "peer-host".into(),
                     version: "0.1.0".into(),
                     daemon_url: "ws://peer:7070".into(),
+                    home_dir: String::new(),
                 }],
                 sessions: vec![sample_session()],
             },