fix(downloads): rewire MaintenanceMenu to the downloads pipeline

The maintenance dropdown in Subscriptions → Downloads was wired to the
filesystem-import pipeline (POST /api/import/retry-failed +
POST /api/import/clear-stuck) — the subtitles even said so ("Re-enqueue
every failed import task"), but it was contextually misplaced. From the
Downloads view "Retry failed" queued nothing the operator could see
because the action operated on import_task rows, not download_event
rows. Import-pipeline maintenance is already reachable from Settings →
Imports (ImportTaskList.vue), so removing the import wiring loses
nothing.

Rewired:
- "Retry failed" → bulk-retries the failing-sources list, same loop as
  FailingSourcesCard's RETRY ALL (sourcesStore.checkNow per source).
  Subtitle now matches: "Re-queue every currently failing source".
- "Force recovery sweep" → triggers recover_stalled_download_events on
  demand via a new POST /api/downloads/recover-stalled endpoint. The
  sweep also runs every 5 min on Beat; this is the manual fallback so
  the operator doesn't have to wait for the next tick to clear newly
  stranded events.

MaintenanceMenu is now stateless — emits retry-failed and recover-
stalled. DownloadsTab owns the handlers (reuses the existing
onRetryAll; new onRecoverStalled with a delayed refresh so swept rows
land in the failing rollup).

Operator-flagged 2026-05-29 — "the retry failed button in the
maintenance dropdown doesn't appear to queue anything but manual
requeues works."

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/components/subscriptions/DownloadsTab.vue

@@ -22,7 +22,10 @@
           <v-icon>mdi-refresh</v-icon>
           <v-tooltip activator="parent" location="top">Refresh</v-tooltip>
         </v-btn>
-        <MaintenanceMenu @refresh="refresh" />
+        <MaintenanceMenu
+          @retry-failed="onRetryAll(store.failing)"
+          @recover-stalled="onRecoverStalled"
+        />
       </div>
 
       <div class="fc-dl__controls">
@@ -207,6 +210,24 @@ async function onRetryAll(sources) {
   toast({ text: parts.join(', ') || 'Nothing to retry', type: 'info' })
 }
 
+// Manual trigger for recover_stalled_download_events. The sweep runs on
+// Beat every 5 min; this lets the operator force-clear stuck pending/
+// running events on demand. Fire-and-forget: the API returns 202 once the
+// task is dispatched, and we refresh after a few seconds so swept rows
+// show up in the failing rollup.
+async function onRecoverStalled() {
+  try {
+    await store.recoverStalled()
+    toast({
+      text: 'Recovery sweep queued — refreshing in a few seconds',
+      type: 'success',
+    })
+    setTimeout(refresh, 4000)
+  } catch (e) {
+    toast({ text: `Sweep failed: ${e?.detail || e?.message || e}`, type: 'error' })
+  }
+}
+
 // Live auto-refresh: while any download is queued or running, poll the
 // stats + first page every 4s so the operator can watch events succeed/
 // fail in real time without hitting Refresh. Polling stops automatically