feat(saas): add quota middleware and usage aggregation worker

B1.3 Quota middleware:
- quota_check_middleware for relay route chain
- Checks monthly relay_requests quota before processing
- Gracefully degrades on billing service failure

B1.5 AggregateUsageWorker:
- Aggregates usage_records into billing_usage_quotas monthly
- Supports single-account and all-accounts modes
- Scheduled hourly via Worker dispatcher (6 workers total)

crates/zclaw-saas/src/main.rs

@@ -11,6 +11,7 @@ use zclaw_saas::workers::cleanup_refresh_tokens::CleanupRefreshTokensWorker;
 use zclaw_saas::workers::cleanup_rate_limit::CleanupRateLimitWorker;
 use zclaw_saas::workers::record_usage::RecordUsageWorker;
 use zclaw_saas::workers::update_last_used::UpdateLastUsedWorker;
+use zclaw_saas::workers::aggregate_usage::AggregateUsageWorker;
 
 #[tokio::main]
 async fn main() -> anyhow::Result<()> {
@@ -44,7 +45,8 @@ async fn main() -> anyhow::Result<()> {
     dispatcher.register(CleanupRateLimitWorker);
     dispatcher.register(RecordUsageWorker);
     dispatcher.register(UpdateLastUsedWorker);
-    info!("Worker dispatcher initialized (5 workers registered)");
+    dispatcher.register(AggregateUsageWorker);
+    info!("Worker dispatcher initialized (6 workers registered)");
 
     // 优雅停机令牌 — 取消后所有 SSE 流和长连接立即终止
     let shutdown_token = CancellationToken::new();