feat: implement background job system with queue, worker, scheduler, and handlers

- Add job queue abstraction (InMemoryQueue and Redis/BullMQ adapter)
- Add polling worker with retry logic and exponential backoff
- Add 6 job handlers: darkwatch.scan, voiceprint.batch, hometitle.scan,
  removebrokers.process, reports.generate, notifications.send
- Add cron-based scheduler with tier-appropriate frequencies
  (Basic/Plus/Premium)
- Add tRPC scheduler router for admin (runJobNow, getJobStatus, etc.)
- Add entry point with graceful shutdown support
- Achieve 100% test pass rate for new job system

web/src/server/jobs/handlers/darkwatch.scan.ts

@@ -0,0 +1,38 @@
+import { eq, and } from "drizzle-orm";
+import { db } from "~/server/db";
+import { watchlistItems, subscriptions } from "~/server/db/schema";
+import { runScan } from "~/server/services/darkwatch.service";
+
+interface DarkWatchScanPayload {
+  userId: string;
+  subscriptionId: string;
+}
+
+export async function handler(payload: DarkWatchScanPayload): Promise<void> {
+  const { userId, subscriptionId } = payload;
+
+  const sub = await db
+    .select()
+    .from(subscriptions)
+    .where(and(eq(subscriptions.id, subscriptionId), eq(subscriptions.status, "active")))
+    .limit(1)
+    .then((r) => r[0]);
+
+  if (!sub) {
+    console.warn(`[darkwatch.scan] Subscription ${subscriptionId} not found or inactive, skipping`);
+    return;
+  }
+
+  const items = await db
+    .select()
+    .from(watchlistItems)
+    .where(and(eq(watchlistItems.subscriptionId, subscriptionId), eq(watchlistItems.isActive, true)));
+
+  if (items.length === 0) {
+    console.log(`[darkwatch.scan] No active watchlist items for subscription ${subscriptionId}`);
+    return;
+  }
+
+  await runScan(userId);
+  console.log(`[darkwatch.scan] Completed scan for subscription ${subscriptionId}`);
+}