fix: use relative API URL in feature branch UI to eliminate CORS errors

Browser requests now go to the UI origin and nginx proxies them to the
backend within the cluster. Removes the separate API Ingress host rule
since API traffic no longer needs its own subdomain.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

deploy/overlays/feature/kustomization.yaml

@@ -38,5 +38,5 @@ patches:
         path: /data/config.js
         value: |
           window.__CAMELEER_CONFIG__ = {
-            apiBaseUrl: 'http://BRANCH_SLUG-api.cameleer.siegeln.net/api/v1',
+            apiBaseUrl: '/api/v1',
           };