fix: handle auth errors and JSON parsing in admin panel

- Added proper HTTP status check before JSON parsing in AnalyticsPage
  * Prevents "Unexpected token '<'" error when API returns HTML error pages
  * Throws proper error for non-OK responses

- Enhanced API error handling to treat 403 as auth failure
  * Both 401 and 403 now trigger redirect to login page
  * Clears expired admin tokens automatically
  * Prevents users from staying on admin pages with expired sessions

These fixes resolve:
1. JSON parse errors when fetching Umami config
2. 403 Forbidden errors not redirecting to login
3. Backend version display issues due to auth failures

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

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

frontend/src/config/api.ts

@@ -82,13 +82,13 @@ api.interceptors.response.use(
       }
     }
     
-    if (error.response?.status === 401) {
+    if (error.response?.status === 401 || error.response?.status === 403) {
       // Check if it's an admin route
       const isAdminRoute = error.config?.url?.includes('/admin');
       const currentPath = window.location.pathname;
       
       if (isAdminRoute) {
-        // Clear admin token on unauthorized
+        // Clear admin token on unauthorized or forbidden
         Cookies.remove(ADMIN_TOKEN_KEY);
         // Only redirect if we're not already on the admin login page
         if (!currentPath.includes('/admin/login')) {

frontend/src/pages/admin/AnalyticsPage.tsx

@@ -76,6 +76,11 @@ export const AnalyticsPage: React.FC = () => {
     const fetchUmamiConfig = async () => {
       try {
         const response = await fetch(`${import.meta.env.VITE_API_URL}/api/public/settings`);
+        
+        if (!response.ok) {
+          throw new Error(`HTTP error! status: ${response.status}`);
+        }
+        
         const settings = await response.json();
         
         // Check if Umami is enabled in admin settings