fix(palacms): use palacms image

[cuisongliu]

Summary

• switch PalacMS runtime image from the Primo image to ghcr.io/palacms/palacms:v3.0.0-beta.1
• keep existing PalacMS metadata, assets, and platform declaration unchanged

Validation

• ruby -e 'require "yaml"; YAML.load_stream(File.read("/Users/cuisongliu/workspace/templates-secondbatch-main-0615/template/palacms/index.yaml")); puts "yaml ok"'\n- git diff --check\n- checked no :latest, digest, or labring-actions/templates URL was introduced in template/palacms

[cuisongliu]

Closing this PR because ghcr.io/palacms/palacms:v3.0.0-beta.1 is not publicly pullable in CI. Both amd64 and arm64 build jobs fail with GHCR token 403, and no Docker Hub replacement is published. Keeping the existing public ghcr.io/primocms/primo:3.2.0 image for now; PalacMS should be handled separately if a public runtime image is published.