feat(04-01): implement CAS checkout, lock release, stale recovery, and migration 16

- Rewrite checkoutTask to use runId-based CAS with checkout_run_id IS NULL guard
- Add releaseTaskLock and recoverStaleLocks methods
- Add lock release in finishRun and cancelRunForDeletion exit paths
- Add migration 16: pending_wakes to wakeup_requests cutover with DROP TABLE
- Replace all pending_wakes references with wakeup_requests
- Add wakeup lifecycle CRUD: enqueue, claim, complete, defer, promote, list
- Update api-server, orchestration-service, worker-service callers
- Update existing database.test.ts for new checkoutTask signature

src/main/api-server.ts

@@ -355,7 +355,7 @@ export class AgentApiServer {
         return;
       }
       const previousStatus = task.status;
-      const success = this.db.checkoutTask(params.issueId!, agentId);
+      const success = this.db.checkoutTask(params.issueId!, token.runId);
       if (!success) {
         this.json(res, 409, { error: "Task cannot be checked out — already assigned or not in valid status" });
         return;