feat(triage): failed-processing triage — probe errored files, flag defects, recover (#125 C1-C3)

An errored GPU job's stored reason is a suspicion; the file probe is the
verdict. A 15-min beat sweep (triage_gpu_errors) runs verify_integrity's own
probe (sha256 + decode) on each errored image ONCE and writes both verdicts:
ImageRecord.integrity_status and the new GpuJob.triage_status ('defect' |
'file_ok', migration 0072). Every classification logs at WARNING so it
surfaces in Logs/System Activity.

- 'defect' rows are excluded from /retry_errors (re-running a known-bad file
  burns agent time re-minting the tombstone); response now reports
  defects_kept and the GpuAgentCard toast says so.
- GET /api/gpu/errors: triage view — reason buckets (classify_reason),
  probe verdicts, per-job detail. POST /errors/triage runs the sweep now.
- POST /api/gpu/errors/<id>/recover: reuses the Layer-2 refetch pattern —
  delete the defective copy + record (full cascade takes the tombstones too)
  and re-poll its subscription Source so a fresh copy re-imports and re-enters
  the pipeline; 'no_source' when nothing pollable resolves.
- New 'Failed processing' card (GpuTriageCard) in Maintenance: verdict counts,
  reason summary, probe-now, defect list with thumbnails + per-image Recover.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

frontend/src/stores/gpu.js

@@ -36,10 +36,32 @@ export const useGpuStore = defineStore('gpu', () => {
   }
 
   // Requeue ONLY the errored jobs (all task types) — the scoped recovery after
-  // an agent fix, without re-running the done library. Returns { requeued }.
+  // an agent fix, without re-running the done library. Triage-confirmed
+  // defects stay put (they recover via recoverImage instead).
+  // Returns { requeued, pruned, defects_kept }.
   async function retryErrors() {
     return await api.post('/api/gpu/retry_errors')
   }
 
-  return { token, rotateToken, status, backfill, reprocess, retryErrors }
+  // Failure-triage view (#125): errored jobs joined with integrity verdicts.
+  // Returns { total, by_class, triage, items }.
+  async function errors() {
+    return await api.get('/api/gpu/errors')
+  }
+
+  // Run the file-probe sweep now instead of waiting out the 15-min beat.
+  async function triageErrors() {
+    return await api.post('/api/gpu/errors/triage')
+  }
+
+  // Recover a defective original: delete the bad copy + record, re-poll its
+  // Source. Returns { status: 'refetch_queued'|'no_source'|'not_found', ... }.
+  async function recoverImage(imageId) {
+    return await api.post(`/api/gpu/errors/${imageId}/recover`)
+  }
+
+  return {
+    token, rotateToken, status, backfill, reprocess, retryErrors,
+    errors, triageErrors, recoverImage,
+  }
 })