feat(gpu): "Retry errored jobs" — scoped requeue of errors only

After an agent-side fix (e.g. the short-video sampler), the errored jobs
(~2.8k) have exhausted their 3 attempts and stay parked: backfill skips
images that already have a job, and /reprocess is the nuclear option (it
resets the 179k DONE jobs too). There was no way to re-run just the errors.

POST /api/gpu/retry_errors resets every status='error' job (all task types)
to pending with attempts=0 and the stored error cleared — a small inline
UPDATE that returns {requeued: n} so the UI toast can show the count.

UI: a "Retry errored jobs" button on the GPU-agent card, right under the
queue tiles; disabled when errored==0. With the agent now logging ffmpeg's
stderr on failure, retrying also reveals which errors were real vs victims
of the fps-filter bug.

Test: retry_errors requeues the errored job (fresh attempts, error cleared)
and leaves done work untouched; asserts via column selects (Core-DML
gotcha), not ORM refresh.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/stores/gpu.js

@@ -35,5 +35,11 @@ export const useGpuStore = defineStore('gpu', () => {
     return await api.post('/api/gpu/reprocess', { body: { task } })
   }
 
-  return { token, rotateToken, status, backfill, reprocess }
+  // Requeue ONLY the errored jobs (all task types) — the scoped recovery after
+  // an agent fix, without re-running the done library. Returns { requeued }.
+  async function retryErrors() {
+    return await api.post('/api/gpu/retry_errors')
+  }
+
+  return { token, rotateToken, status, backfill, reprocess, retryErrors }
 })