Migrate github-pr-review skill into agent-skills (spec-compliant)

[rubambiza]

Parent epic: rossoctl/rossoctl#2149 · Companion: rossoctl/automation#26 · Land this first.

Goal

Migrate the github:pr-review skill from kagenti/kagenti/.claude/skills/github:pr-review/ into this repo as a self-contained, spec-compliant skill importable via the /plugin marketplace. Part of rossoctl/rossoctl#2149.

Today the bot reads the skill from a hard-coded path in the on-host kagenti/kagenti clone, kept current only by a nightly pull. Bundling it here makes it version-controlled, importable, and usable beyond the kagenti org.

Scope

• Create skills/github-pr-review/ (single self-contained skill: SKILL.md + optional reference/).
• Port the review workflow from the current single SKILL.md. The skill is self-contained — it drives the review with inline gh/git calls and does not invoke the pr-review-*.sh orchestration scripts — so those scripts stay canonical in kagenti/automation and are not bundled here (avoids duplicating kagenti-specific orchestration into the reusable repo).
• Register a github-pr-review plugin in .claude-plugin/marketplace.json.
• Verify import via /plugin and update via /reload-plugins.

Naming

Rename github:pr-review -> github-pr-review (flat hyphen, drop the colon): keeps the github family prefix, is portable, and matches the agent-skills flat-naming convention. This sets the github:* -> github-* precedent for the other 7 github:* skills (dependabot, issues, last-week, last-week-org, my-status, prs, streamer) that may migrate later.

Single source of truth

This repo is the SOLE home for the github-pr-review SKILL.md — it is NOT duplicated into kagenti/automation. automation keeps only the orchestration scripts + standing order and references this skill (rossoctl/automation#26), avoiding two-copy drift.

Companion

• Epic: chore: Migrate github-pr-review skill to agent-skills repo rossoctl#2149.