feat: add Gateway page and Runs page with real-time updates

- Implemented a new Gateway page that provides a uniform ingress for deployed agents.
- Created a Runs page that lists recent pipeline executions with auto-refresh and error handling.
- Added a RunsListener component to handle real-time notifications for new runs via SSE.
- Updated the AppSidebar to include links to the new Gateway and Runs pages.
- Enhanced FlowNode component to improve status display and styling.
- Introduced EmptySection component for consistent empty state presentation.
- Updated API utility to include a new endpoint for the runs stream.

web/app/agents/view/page.tsx

@@ -88,6 +88,12 @@ function AgentDetail() {
 
   useEffect(() => {
     load();
+    // Reload recent runs whenever any run is dispatched (manual / agent /
+    // GitHub push). Cheap — `load()` is one round-trip.
+    const es = new EventSource(api.runsStreamURL());
+    es.onmessage = () => load();
+    es.onerror = () => {};
+    return () => es.close();
     // eslint-disable-next-line react-hooks/exhaustive-deps
   }, [id]);