feat: replace nginx-ingress with Traefik and Gateway API

[bussyjd]

Summary

• Replace nginx-ingress controller with Traefik 38.0.2 using Kubernetes Gateway API
• Address nginx-ingress deprecation (end of maintenance March 2026)
• Migrate all Ingress resources to HTTPRoute format

Changes

• Remove --disable=traefik from k3d config to use k3s built-in Traefik
• Replace nginx-ingress helm release with Traefik 38.0.2 in infrastructure helmfile
• Configure Gateway API provider with cross-namespace routing support
• Add GatewayClass and Gateway resources via Traefik helm chart
• Convert all Ingress resources to HTTPRoute format:
  • eRPC: /rpc path routing
  • obol-frontend: / path routing
  • ethereum: /execution and /beacon path routing with URL rewrite
  • aztec: namespace-based path routing with URL rewrite
  • helios: namespace-based path routing with URL rewrite
• Disable legacy Ingress in service helm values

Test plan

• Stack init and up with new Traefik configuration
• Verify GatewayClass is accepted
• Verify Gateway is programmed with correct listeners
• Verify HTTPRoutes are accepted and refs resolved
• Test frontend routing via http://obol.stack/
• Test eRPC routing via http://obol.stack/rpc
• Test network-specific routes after network install

Closes #125