fix(auth): use API_INTERNAL_URL in userGroup hook

The userGroup hook was hardcoding http://localhost:8080 instead of
reading API_INTERNAL_URL from the environment. In Docker this caused
the /api/users/me fetch to fail silently, leaving event.locals.user
unset and triggering the handleAuth guard to redirect every page to
/login — including the login form action itself, creating an infinite
redirect loop.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/hooks.server.ts

@@ -27,7 +27,8 @@ const userGroup: Handle = async ({ event, resolve }) => {
 
     if (auth) {
         try {
-            const response = await fetch('http://localhost:8080/api/users/me', {
+            const apiUrl = env.API_INTERNAL_URL || 'http://localhost:8080';
+            const response = await fetch(`${apiUrl}/api/users/me`, {
                         headers: { Authorization: auth }
 
             });