Add real-time session updates via Server-Sent Events

Implements push-based real-time updates for the Sessions page. New sessions now appear instantly without manual reload or polling.

Changes:
- Add SSE event emitter for session creation notifications
- Create SSE stream endpoint at /api/websites/[id]/sessions/stream
- Emit session events in tracking endpoint when sessions are created
- Add useSessionStream hook to connect to SSE and invalidate queries
- Fix LoadingPanel to prevent flicker during background refetches

src/components/hooks/index.ts

@@ -79,6 +79,7 @@ export * from './useNavigation';
 export * from './usePagedQuery';
 export * from './usePageParameters';
 export * from './useRegionNames';
+export * from './useSessionStream';
 export * from './useSlug';
 export * from './useSticky';
 export * from './useTimezone';

src/components/hooks/useSessionStream.ts

@@ -0,0 +1,18 @@
+import { useEffect } from 'react';
+import { useQueryClient } from '@tanstack/react-query';
+
+export function useSessionStream(websiteId: string) {
+  const queryClient = useQueryClient();
+
+  useEffect(() => {
+    if (!websiteId) return;
+
+    const eventSource = new EventSource(`/api/websites/${websiteId}/sessions/stream`);
+
+    eventSource.onmessage = () => {
+      queryClient.invalidateQueries({ queryKey: ['sessions'] });
+    };
+
+    return () => eventSource.close();
+  }, [websiteId, queryClient]);
+}