Fix React error #130 - Remove authentication race condition

- Remove setTimeout delays in AdminAuthContext login function
- Make authentication state updates synchronous
- Replace setTimeout navigation with state-based navigation in AdminLoginPage
- Add proper error handling and component lifecycle management in CreateEventPage
- Prevent navigation if component unmounts during async operations

This fixes the issue where users would see React error #130 during login
and couldn't create events or save settings.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/src/contexts/AdminAuthContext.tsx

@@ -36,13 +36,19 @@ export const AdminAuthProvider: React.FC<AdminAuthProviderProps> = ({ children }
   useEffect(() => {
     // Check if user has a valid token on mount
     const checkAuth = async () => {
-      const token = getAuthToken(true);
-      if (token) {
-        // For now, just assume the token is valid
-        // TODO: Validate token with backend and get user info
-        setIsAuthenticated(true);
+      try {
+        const token = getAuthToken(true);
+        if (token) {
+          // For now, just assume the token is valid
+          // TODO: Validate token with backend and get user info
+          setIsAuthenticated(true);
+        }
+      } catch (error) {
+        console.error('Auth check error:', error);
+        setError('Failed to check authentication');
+      } finally {
+        setIsLoading(false);
       }
-      setIsLoading(false);
     };
     
     checkAuth();
@@ -52,10 +58,7 @@ export const AdminAuthProvider: React.FC<AdminAuthProviderProps> = ({ children }
     // Token is already stored in cookie by authService
     setUser(user);
     setError(null);
-    // Small delay to ensure state is properly updated
-    setTimeout(() => {
-      setIsAuthenticated(true);
-    }, 100);
+    setIsAuthenticated(true);
   };
 
   const logout = () => {