Fix: persist SSO auth token on root route loader (#12784)

### What problem does this PR solve?

This PR fixes SSO/OIDC login persistence after the Vite migration
#12568. Because wrappers are ignored by React Router, the OAuth callback
never stored the auth token in localStorage, causing auth to only work
while ?auth= stayed in the URL. We move that logic into a route loader
and remove the Bearer prefix for the signed token so the backend accepts
it.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

Contribution during my time at RAGcon GmbH.

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

web/src/utils/authorization-util.ts

@@ -49,9 +49,7 @@ const storage = {
 
 export const getAuthorization = () => {
   const auth = getSearchValue('auth');
-  const authorization = auth
-    ? 'Bearer ' + auth
-    : storage.getAuthorization() || '';
+  const authorization = auth ? auth : storage.getAuthorization() || '';
 
   return authorization;
 };