chore: reduce SKILL.md from 3,100 to ~500 words, consider splitting

[CybotTM]

Quality Review Finding

Per marketplace tracking issue, this skill has critical quality issues:

Word count: 3,100 (target: <500)

Issues

1. Massive scope creep — covers repository setup, Dependabot/Renovate, GitHub Actions, TYPO3 extensions, merge strategy, OpenSSF Scorecard, CodeQL, and auto-merge troubleshooting
2. No clear "Overview" section — jumps into diagnostics immediately
3. 50+ lines of GraphQL/bash commands in quick diagnostics — this is reference material, not skill content

Recommended Actions

• Consider splitting into sub-skills: github-setup, github-dependabot, github-security
• Move diagnostic commands to references/diagnostics.md
• Keep main skill to ~500 words: Overview + When to Use + Quick Fix Table
• Rewrite frontmatter description: "Use when configuring GitHub repositories, troubleshooting auto-merge, setting up branch protection, or managing GitHub Actions."