fix: update Pastel UI to use internal API URL

Changed Pastel UI environment variable to use internal Docker
network communication instead of external HTTPS:
- Changed from NEXT_PUBLIC_API_URL/NEXT_PUBLIC_APP_URL to PASTEL_API_URL
- Use internal container name: http://pastel_api:3000
- Removes dependency on external domain resolution
- Improves performance by avoiding Traefik proxy for internal calls

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

kit/compose.yaml

@@ -115,8 +115,7 @@ services:
     healthcheck:
       disable: true
     environment:
-      NEXT_PUBLIC_API_URL: https://${KIT_PASTEL_TRAEFIK_HOST}
-      NEXT_PUBLIC_APP_URL: https://${KIT_PASTEL_TRAEFIK_HOST}
+      PASTEL_API_URL: http://pastel_api:3000
     networks:
       - compose_network
     labels: