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/lib/api.ts

@@ -349,6 +349,12 @@ export interface SchedulerStatus {
     daily_budget: number;
     backfill_reserve: number;
   };
+  maintenance: {
+    revalidate_batch: number;
+    revalidate_batch_default: number;
+    min: number;
+    max: number;
+  };
 }
 
 export interface Account {
@@ -474,6 +480,11 @@ export const api = {
     req(`/api/admin/scheduler/jobs/${jobId}/run`, { method: "POST" }),
   runAllSchedulerJobs: (): Promise<{ started: string[] }> =>
     req("/api/admin/scheduler/run-all", { method: "POST" }),
+  updateMaintenanceBatch: (revalidateBatch: number): Promise<{ revalidate_batch: number }> =>
+    req("/api/admin/scheduler/maintenance", {
+      method: "PATCH",
+      body: JSON.stringify({ revalidate_batch: revalidateBatch }),
+    }),
 
   // --- onboarding / admin ---
   requestAccess: (email: string): Promise<{ status: string }> =>