fix: include admin homepage in route discovery

[arch-err]

Summary

• switch Homepage HTTPRoute discovery annotations from scalar gethomepage.dev/instance to named gethomepage.dev/instance.<name> entries
• tag dashboard-visible routes for both their gateway instance and the admin instance
• set the admin Homepage instanceName to admin
• clean up stale comments around instance filtering

Verification

• helm lint kubernetes/platform -f kubernetes/apps.yaml
• helm template platform kubernetes/platform -f kubernetes/apps.yaml + YAML parse
• helm lint kubernetes/platform -f kubernetes/infra.yaml
• helm template platform kubernetes/platform -f kubernetes/infra.yaml + YAML parse
• confirmed rendered manifests contain named instance annotations and zero scalar gethomepage.dev/instance annotations