feat(scheduler): admin-tunable maintenance re-validation batch size

Expose the maintenance job's rolling re-validation batch (videos re-checked per
run) as an admin control on the Scheduler dashboard, stored in app_state
(migration 0018; NULL = the env/config default). The job reads the effective
value each run via a state helper, clamped to a sane range. Trilingual.

frontend/src/components/Scheduler.tsx

@@ -212,6 +212,60 @@ function JobRow({
   );
 }
 
+function MaintenanceSettings({
+  m,
+  onSave,
+  saving,
+}: {
+  m: SchedulerStatus["maintenance"];
+  onSave: (batch: number) => void;
+  saving: boolean;
+}) {
+  const { t } = useTranslation();
+  const [val, setVal] = useState(String(m.revalidate_batch));
+  useEffect(() => setVal(String(m.revalidate_batch)), [m.revalidate_batch]);
+
+  function save() {
+    const n = parseInt(val, 10);
+    if (Number.isFinite(n) && n >= m.min && n <= m.max && n !== m.revalidate_batch) onSave(n);
+  }
+  const dirty = String(m.revalidate_batch) !== val;
+
+  return (
+    <div className="glass-card rounded-xl p-4">
+      <div className="flex items-center gap-2 text-sm flex-wrap">
+        <Database className="w-4 h-4 text-muted shrink-0" />
+        <Tooltip hint={t("scheduler.maintenance.batchHint")}>
+          <span className="underline decoration-dotted decoration-muted/40 underline-offset-4 cursor-help">
+            {t("scheduler.maintenance.batchLabel")}
+          </span>
+        </Tooltip>
+        <span className="flex-1" />
+        <input
+          type="number"
+          min={m.min}
+          max={m.max}
+          step={1000}
+          value={val}
+          onChange={(e) => setVal(e.target.value)}
+          onKeyDown={(e) => e.key === "Enter" && save()}
+          className="w-28 bg-card border border-border rounded px-2 py-1 text-sm tabular-nums outline-none focus:border-accent"
+        />
+        <button
+          onClick={save}
+          disabled={!dirty || saving}
+          className="glass-card glass-hover px-3 py-1.5 rounded-lg text-sm disabled:opacity-40 transition"
+        >
+          {t("common.save")}
+        </button>
+      </div>
+      <div className="text-[11px] text-muted mt-1.5">
+        {t("scheduler.maintenance.batchNote", { default: m.revalidate_batch_default.toLocaleString() })}
+      </div>
+    </div>
+  );
+}
+
 function Stat({
   icon: Icon,
   label,
@@ -285,6 +339,10 @@ export default function Scheduler() {
       qc.invalidateQueries({ queryKey: ["scheduler"] });
     },
   });
+  const batchMut = useMutation({
+    mutationFn: (v: number) => api.updateMaintenanceBatch(v),
+    onSuccess: () => qc.invalidateQueries({ queryKey: ["scheduler"] }),
+  });
 
   if (q.isLoading && !data)
     return <div className="p-8 text-muted">{t("scheduler.loading")}</div>;
@@ -432,6 +490,16 @@ export default function Scheduler() {
           <div className="text-[11px] text-muted mt-1.5">{t("scheduler.quotaNote")}</div>
         </div>
       </div>
+
+      {/* Maintenance settings */}
+      <div>
+        <div className="text-xs uppercase tracking-wide text-muted mb-2">{t("scheduler.maintenance.title")}</div>
+        <MaintenanceSettings
+          m={data.maintenance}
+          onSave={(batch) => batchMut.mutate(batch)}
+          saving={batchMut.isPending}
+        />
+      </div>
     </div>
   );
 }