Revert BASE_URL to empty - Headlamp expects path not full URL

Headlamp's BASE_URL config expects a path prefix (e.g., "/headlamp") or empty
string, not a full URL. Since Headlamp is deployed at the domain root, BASE_URL
should be empty.

The OIDC redirect URIs in Pocket ID are correctly configured and the user has
been added to the headlamp group, which should resolve the authentication issue.

Related to DEV-324

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/headlamp/deployment.yaml

@@ -27,7 +27,7 @@ spec:
           protocol: TCP
         env:
         - name: HEADLAMP_CONFIG_BASE_URL
-          value: "https://headlamp.basicstack.de"
+          value: ""
         - name: HEADLAMP_CONFIG_OIDC_IDP_ISSUER_URL
           value: https://auth.basicstack.de
         - name: HEADLAMP_CONFIG_OIDC_CLIENT_ID