[caelaxie]

Summary

Adds GitHub Actions CI for the Grok Build port, following the workflow in agy-pstack.

The job checks out the repo, installs the grok CLI the same way that port installs agy (resolve the published version, cache the binary, install on a cache miss), then validates this plugin:

• grok plugin validate on the checkout and on the installed copy
• grok plugin install . --trust and grok plugin list --json (name and version)
• grok inspect --json for the enabled plugin plus the skills and agents Grok actually loaded
• plugin.json against the shared plugin schema, with Grok's kebab-case name rule
• skill and agent frontmatter (name, description, Grok's name normalization and frontmatter limits, and the plugin-agent restrictions on mcpServers, hooks, and permissionMode: bypassPermissions)
• the poteto-mode principle and playbook indexes
• shell syntax, plus the existing Bun typecheck and tests under skills/poteto-mode/scripts

Plugin content is unchanged.

Test plan

• Ran the validate step locally against grok 1.0.60 (57 skills, 2 agents, 23 playbooks)
• Ran bun run typecheck and bun run test in skills/poteto-mode/scripts (68 tests)
• CI on this pull request is green: https://github.com/pstack-ports/grok-pstack/actions/runs/38892036426