Add authentication, Redis pub/sub, and error handling to SSE

Improvements:
- Add Redis pub/sub support for multi-server deployments
- Add authentication check to SSE stream endpoint
- Add 30s heartbeat keepalive for long-lived connections
- Implement exponential backoff reconnection logic in client
- Fix TypeScript types (websiteId optional, timer types)
- Use specific query key invalidation instead of broad match
- Fix undefined access in session-events listener map

src/components/hooks/useSessionStream.ts

@@ -1,18 +1,61 @@
-import { useEffect } from 'react';
+import { useEffect, useRef } from 'react';
 import { useQueryClient } from '@tanstack/react-query';
 
-export function useSessionStream(websiteId: string) {
+const MAX_RETRY_DELAY = 30000;
+const INITIAL_RETRY_DELAY = 1000;
+
+export function useSessionStream(websiteId?: string) {
   const queryClient = useQueryClient();
+  const retryCountRef = useRef(0);
+  const retryTimeoutRef = useRef<ReturnType<typeof setTimeout> | null>(null);
 
   useEffect(() => {
     if (!websiteId) return;
 
-    const eventSource = new EventSource(`/api/websites/${websiteId}/sessions/stream`);
+    let eventSource: EventSource | null = null;
+    let isMounted = true;
 
-    eventSource.onmessage = () => {
-      queryClient.invalidateQueries({ queryKey: ['sessions'] });
+    const connect = () => {
+      if (!isMounted) return;
+
+      eventSource = new EventSource(`/api/websites/${websiteId}/sessions/stream`);
+
+      eventSource.onmessage = event => {
+        try {
+          const data = JSON.parse(event.data);
+          if (data.sessionId) {
+            retryCountRef.current = 0;
+            queryClient.invalidateQueries({ queryKey: ['sessions', { websiteId }] });
+          }
+        } catch (error) {
+          // eslint-disable-next-line no-console
+          console.error('Failed to parse session event:', error);
+        }
+      };
+
+      eventSource.onerror = () => {
+        eventSource?.close();
+
+        if (!isMounted) return;
+
+        const delay = Math.min(
+          INITIAL_RETRY_DELAY * Math.pow(2, retryCountRef.current),
+          MAX_RETRY_DELAY,
+        );
+        retryCountRef.current += 1;
+
+        retryTimeoutRef.current = setTimeout(connect, delay);
+      };
     };
 
-    return () => eventSource.close();
+    connect();
+
+    return () => {
+      isMounted = false;
+      if (retryTimeoutRef.current) {
+        clearTimeout(retryTimeoutRef.current);
+      }
+      eventSource?.close();
+    };
   }, [websiteId, queryClient]);
 }