fix: Replace Ingress with HTTPRoute (Gateway API)

Switch from Ingress to HTTPRoute for Gateway API compatibility.

Changes:
- Remove k8s/ingress.yaml
- Add k8s/httproute.yaml with Gateway API configuration
- Update kustomization.yaml to reference httproute.yaml
- Update README.md references from Ingress to HTTPRoute

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via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

README.md

@@ -80,7 +80,7 @@ kubectl port-forward statefulset/antigravity 5800:5800
 open http://localhost:5800
 ```
 
-Or configure Ingress for external access.
+Or configure HTTPRoute (Gateway API) for external access via your domain.
 
 ## Environment Variables