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/common/LoadingPanel.tsx

@@ -28,9 +28,11 @@ export function LoadingPanel({
   ...props
 }: LoadingPanelProps): ReactNode {
   const empty = isEmpty ?? checkEmpty(data);
+  const hasData = data && !empty;
 
-  // Show loading spinner only if no data exists
-  if (isLoading || isFetching) {
+  // Show loading only on initial load when no data exists yet
+  // Don't show loading during background refetches when we already have data
+  if ((isLoading || isFetching) && !hasData) {
     return (
       <Column position="relative" height="100%" width="100%" {...props}>
         <Loading icon={loadingIcon} placement={loadingPlacement} />
@@ -48,8 +50,8 @@ export function LoadingPanel({
     return renderEmpty();
   }
 
-  // Show main content when data exists
-  if (!isLoading && !isFetching && !error && !empty) {
+  // Show content when we have data (even during background refetch)
+  if (hasData) {
     return children;
   }
 

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]);
+}