ci: add sync-skills workflow

[ko3n1g]

Summary

This PR sets up the skills infrastructure and agent-compatible entrypoint for the RL repo:

• Add .github/workflows/sync-skills.yml: A workflow that keeps agent tool directories in sync on every push to main.
• Rename CLAUDE.md → AGENTS.md: The project instructions file is renamed to the standard entrypoint recognized by agent frameworks (OpenAI Codex, Claude Code, etc.).
• Move .claude/skills/ → skills/: The skills directory is moved to the top-level, making skills accessible to all agent frameworks, not just Claude Code.

Background

There is no common standard for markdown file discovery across agent frameworks — each tool looks in a different place. This PR addresses that gap by coupling the generic AGENTS.md / skills/ layout with a sync job that runs on push to main, so every agent runtime finds the files it expects without per-framework duplication.

Example

After this PR, the repo layout is:

AGENTS.md          ← project instructions (was CLAUDE.md)
skills/            ← shared skills directory (was .claude/skills/)
  code-style/
  config-conventions/
  copyright/
  docs/
  error-handling/
  review-pr/
  testing/
.github/workflows/
  sync-skills.yml  ← keeps skills/ in sync

[copy-pr-bot]

Auto-sync is disabled for ready for review pull requests in this repository. Workflows must be run manually.

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[ko3n1g]

/ok to test