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/turn.rs

@@ -169,7 +169,12 @@ pub fn emit_turn_end(bus: &Bus, outcome: &TurnOutcome) {
 /// Block until the bound `~/.claude/` dir contains a session, polling
 /// `claude_dir` on a `poll_ms` interval (min 2s). Flips `state` to
 /// `Online` when login lands; caller resumes its serve loop.
-pub async fn wait_for_login(claude_dir: &Path, state: Arc<Mutex<LoginState>>, poll_ms: u64) {
+pub async fn wait_for_login(
+    claude_dir: &Path,
+    state: Arc<Mutex<LoginState>>,
+    bus: &Bus,
+    poll_ms: u64,
+) {
     tracing::warn!(
         claude_dir = %claude_dir.display(),
         "no claude session — staying in partial-run mode (web UI only)"
@@ -180,6 +185,7 @@ pub async fn wait_for_login(claude_dir: &Path, state: Arc<Mutex<LoginState>>, po
         if login::has_session(claude_dir) {
             tracing::info!("claude session detected — entering turn loop");
             *state.lock().unwrap() = LoginState::Online;
+            bus.emit_status("online");
             return;
         }
     }