surface rate_limited status as red badge on per-agent page and dashboard

- add rate_limited: Arc<AtomicBool> to Bus; set/cleared by emit_status
- write/remove sentinel file hyperhive-rate-limited in state dir so host-side
  dashboard can detect it without a live socket call
- api_state returns status=rate_limited when flag is set (cold-load accurate)
- ALIVE_LABELS gains rate_limited entry (⊘ red chip) on per-agent page
- ContainerView gains rate_limited: bool read from sentinel file
- dashboard container row shows ⊘ rate limited badge (red) ahead of needs_login

Closes #24

hive-c0re/assets/app.js

@@ -531,6 +531,10 @@
       if (pending) {
         head.append(el('span', { class: 'pending-state' },
           el('span', { class: 'spinner' }, '◐'), ' ', pending + '…'));
+      } else if (c.rate_limited) {
+        head.append(el('span',
+          { class: 'badge badge-rate-limited', title: 'API rate-limited — harness is parked, will retry automatically' },
+          '⊘ rate limited'));
       } else if (c.needs_login) {
         head.append(el('a',
           { class: 'badge badge-warn', href: url, target: '_blank', rel: 'noopener' },