fix: normalize OIDC issuer URL to avoid double slashes

The OIDC issuer URL in .env ends with a trailing slash, which caused
the authorize endpoint to have a double slash (//authorize).

- Normalize issuer URL by removing trailing slash before appending path
- Applied to both LoginPage.tsx and CallbackPage.tsx
- Fixes Authentik 'not found' error on login redirect

apps/web/src/pages/CallbackPage.tsx

@@ -35,7 +35,8 @@ export default function CallbackPage() {
 
         setStatus('Exchanging code for token...')
 
-        const tokenResponse = await fetch(`${OIDC_ISSUER}/token/`, {
+        const issuer = OIDC_ISSUER.endsWith('/') ? OIDC_ISSUER.slice(0, -1) : OIDC_ISSUER
+        const tokenResponse = await fetch(`${issuer}/token/`, {
           method: 'POST',
           headers: {
             'Content-Type': 'application/x-www-form-urlencoded',