feat(control,api,ui): worker liveness + run event stream (phase 3)

- worker: heartbeat every loop pass (workers registry); reaper pass
  every ~15s marks a silent worker's running runs crashed and flips
  agents stuck in 'working' to crashed (paused/blocked keep their
  still-accurate status). Idempotent via finish_run's running-guard;
  any surviving worker can reap; no auto-requeue (half-done runs may
  have pushed). Dead workers' registry rows are dropped once settled.
- api: GET /projects/{p}/agents/{name}/events - the persisted
  stream-json event log, oldest-first, cursor-paged by row id;
  AgentOut exposes session_id/worker_id
- frontend: Run events panel in the run detail (assistant text, tool
  chips, result footer with cost/turns, runner notices, raw lines),
  cursor-appended on the existing 5s poll; 'Crashed' filter + danger
  badge; crashed agents show their frozen last frame ('last output
  before crash'); static export regenerated

Suite 290 -> 296 green; next build clean.

frontend/components/sections/AgentsSection.tsx

@@ -144,11 +144,12 @@ export function AgentsSection() {
                             </div>
                           </td>
                         </tr>
-                        {a.status === "working" && a.last_output?.trim() && (
+                        {(a.status === "working" || a.status === "crashed") && a.last_output?.trim() && (
                           <tr>
                             <td colSpan={6} style={{ paddingTop: 0 }}>
                               <div className="faint" style={{ fontSize: "var(--text-xs)", marginBottom: 4 }}>
-                                live output{a.output_at ? ` · ${timeAgo(a.output_at)}` : ""}
+                                {a.status === "crashed" ? "last output before crash" : "live output"}
+                                {a.output_at ? ` · ${timeAgo(a.output_at)}` : ""}
                               </div>
                               <pre
                                 className="mono"