agent ui: event-driven status / model / token_usage / turn_state

new LiveEvent variants on the per-agent bus —
status_changed / model_changed / token_usage_changed /
turn_state_changed — replace the per-agent web UI's
/api/state polling for the badge row.

emit sites:
- Bus::set_model → model_changed
- Bus::record_usage → token_usage_changed
- Bus::set_state → turn_state_changed
- turn::wait_for_login → status_changed("online") on creds detect
- post_login_start / post_login_cancel → status_changed("needs_login_*")

per-agent endpoints (post_set_model / post_compact / post_new_session
/ post_cancel_turn / post_login_*) now all return 200; client
drops the post-submit refetch except on login transitions, which
still need /api/state to render the OAuth form + session stream.

client adds dispatch on the four new event kinds, threads
`currentLabel` through so the composer re-enables on a live
status flip, and no longer fires refreshState() from turn_end or
postModel — the events carry the same signal faster.

closes the per-agent half of the dashboard event-channel
refactor; TODO entry dropped.

hive-ag3nt/src/bin/hive-m1nd.rs

@@ -86,7 +86,7 @@ async fn main() -> Result<()> {
                     .await
                 }
                 LoginState::NeedsLogin => {
-                    turn::wait_for_login(&claude_dir, login_state, poll_ms).await;
+                    turn::wait_for_login(&claude_dir, login_state, &bus, poll_ms).await;
                     serve(
                         &cli.socket,
                         Duration::from_millis(poll_ms),