feat(ST-qfpqpxzy): SSE + NavBar stand-by badge voor worker quota-gate

- SSE route: WorkerHeartbeatPayload type + shouldEmit handler voor worker_heartbeat
- solo-store: lowQuotaTokenIds Set<string> + setWorkerLowQuota action
- use-solo-realtime: worker_heartbeat event → setWorkerLowQuota; worker_disconnected verwijdert uit set
- nav-status-indicators: stand-by badge (bg-warning) als alle workers low quota
- docs/runbooks/mcp-integration.md: get_worker_settings + worker_heartbeat tools + pre-flight quota-check sectie

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app/api/realtime/solo/route.ts

@@ -64,7 +64,15 @@ type WorkerPayload = {
   product_id?: string
 }
 
-type NotifyPayload = EntityPayload | JobPayload | WorkerPayload
+type WorkerHeartbeatPayload = {
+  type: 'worker_heartbeat'
+  user_id: string
+  token_id: string
+  last_quota_pct: number | null
+  is_low: boolean
+}
+
+type NotifyPayload = EntityPayload | JobPayload | WorkerPayload | WorkerHeartbeatPayload
 
 function isJobPayload(p: NotifyPayload): p is JobPayload {
   return 'type' in p && (p.type === 'claude_job_enqueued' || p.type === 'claude_job_status')
@@ -74,6 +82,10 @@ function isWorkerPayload(p: NotifyPayload): p is WorkerPayload {
   return 'type' in p && (p.type === 'worker_connected' || p.type === 'worker_disconnected')
 }
 
+function isWorkerHeartbeatPayload(p: NotifyPayload): p is WorkerHeartbeatPayload {
+  return 'type' in p && p.type === 'worker_heartbeat'
+}
+
 function shouldEmit(
   payload: NotifyPayload,
   productId: string,
@@ -90,6 +102,10 @@ function shouldEmit(
     return payload.user_id === userId
   }
 
+  if (isWorkerHeartbeatPayload(payload)) {
+    return payload.user_id === userId
+  }
+
   // M11 (ST-1104): question-events horen op /api/realtime/notifications, niet hier.
   if (payload.entity === 'question') return false