feat(billing): activate real-time quota enforcement pipeline

- Wire relay handler to increment_usage() for JSON responses (tokens + relay_requests)
- Wire relay handler to increment_dimension("relay_requests") for SSE streams
- Add increment_dimension() function for hand_executions/pipeline_runs dimensions
- Schedule AggregateUsageWorker hourly for reconciliation (run_on_start=true)
- Mount mock payment routes in dev mode (ZCLAW_SAAS_DEV=true)

Previously the quota middleware always allowed requests because usage
counters were never incremented. Now relay requests update billing_usage_quotas
in real-time, with the aggregator providing hourly reconciliation.

crates/zclaw-saas/src/main.rs

@@ -386,9 +386,22 @@ async fn build_router(state: AppState) -> axum::Router {
             zclaw_saas::auth::auth_middleware,
         ));
 
-    axum::Router::new()
+    let mut router = axum::Router::new()
         .merge(non_streaming_routes)
-        .merge(relay_routes)
+        .merge(relay_routes);
+
+    // 开发模式挂载 mock 支付页面
+    {
+        let is_dev = std::env::var("ZCLAW_SAAS_DEV")
+            .map(|v| v == "true" || v == "1")
+            .unwrap_or(false);
+        if is_dev {
+            router = router.merge(zclaw_saas::billing::mock_routes());
+            info!("Mock payment routes mounted (dev mode)");
+        }
+    }
+
+    router
         .layer(TraceLayer::new_for_http())
         .layer(cors)
         .with_state(state)