fix(routing): 修正 Worker 心跳时间查询

生产 shadow 发布证明 PostgreSQL 将未显式定型的时间参数推断为 interval，导致 Worker 列表和容量查询返回 SQLSTATE 42883。

改为在 Go 中计算心跳截止时间并以 timestamptz 参数查询，补充真实 PostgreSQL 集成回归。

apps/api/internal/store/execution_pools.go

@@ -101,14 +101,15 @@ func (s *Store) ListWorkers(ctx context.Context, now time.Time) ([]executionpool
 	if now.IsZero() {
 		now = time.Now()
 	}
+	cutoff := now.Add(-workerHeartbeatStaleAfter)
 	rows, err := s.pool.Query(ctx, `
 SELECT worker_id, instance_id, pool_id, endpoint, protocol_version, revision,
        capabilities, allocated_capacity, safe_capacity, heavy_capacity,
        active_tasks, pressure_state, heartbeat_at, load_sampled_at
 FROM gateway_worker_instances
 WHERE status = 'active'
-  AND heartbeat_at > $1 - $2::interval
-ORDER BY pool_id, instance_id`, now, workerHeartbeatStaleAfter.String())
+  AND heartbeat_at > $1::timestamptz
+ORDER BY pool_id, instance_id`, cutoff)
 	if err != nil {
 		return nil, err
 	}
@@ -346,6 +347,7 @@ func (s *Store) ListCapacity(ctx context.Context, now time.Time) ([]executionpoo
 	if now.IsZero() {
 		now = time.Now()
 	}
+	cutoff := now.Add(-workerHeartbeatStaleAfter)
 	rows, err := s.pool.Query(ctx, `
 SELECT pool.pool_id,
        COUNT(worker.instance_id)::int,
@@ -358,12 +360,12 @@ SELECT pool.pool_id,
        COALESCE(MAX(worker.load_sampled_at), $1)
 FROM gateway_execution_pools pool
 LEFT JOIN gateway_worker_instances worker
-  ON worker.pool_id = pool.pool_id
+ ON worker.pool_id = pool.pool_id
  AND worker.status = 'active'
- AND worker.heartbeat_at > $1 - $2::interval
+ AND worker.heartbeat_at > $2::timestamptz
 WHERE pool.state = 'active'
 GROUP BY pool.pool_id
-ORDER BY pool.pool_id`, now, workerHeartbeatStaleAfter.String())
+ORDER BY pool.pool_id`, now, cutoff)
 	if err != nil {
 		return nil, err
 	}