fix: prevent pool exhaustion that caused 4-hour duplicate check stall

The pg pool had max=5 connections shared between Prisma operations and
advisory locks. With 2 account locks held permanently and hash locks
from timed-out (but still running) background work, pool.connect()
would block forever — causing the Turnbase.7z stall.

- Increase pool max from 5 to 15 for headroom
- Add 30s connectionTimeoutMillis so pool.connect() throws instead of
  hanging forever when the pool is exhausted
- On startup, terminate zombie PostgreSQL sessions from previous worker
  instances that hold stale advisory locks

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

worker/src/db/client.ts

@@ -5,7 +5,14 @@ import { config } from "../util/config.js";
 
 const pool = new pg.Pool({
   connectionString: config.databaseUrl,
-  max: 5,
+  // Pool needs headroom for: 2 account advisory locks (held for entire cycle),
+  // up to 2 concurrent hash locks, plus Prisma operations from both accounts.
+  // Previously max=5 caused pool exhaustion and indefinite hangs.
+  max: 15,
+  // Prevent pool.connect() from blocking forever when pool is exhausted.
+  // Throws an error after 30s so the operation can fail and retry instead of
+  // silently hanging for hours (as happened with the Turnbase.7z stall).
+  connectionTimeoutMillis: 30_000,
 });
 
 const adapter = new PrismaPg(pool);