Add an aeon skill (operate an Aeon agent instance) to the extensions registry

Desired Behavior

There is no skill in the extensions registry for operating an Aeon instance. Aeon is an open-source framework that runs a user's own skills on a schedule in GitHub Actions; an agent working inside an Aeon repo currently has no in-registry guidance for it.

Add an aeon skill (operator playbook) in the same shape as the other integration skills here, so an agent can enable/schedule/edit skills, set the STRATEGY.md north star, and debug a skill that isn't firing, using the project's ./aeon CLI and gh.

Acceptance Criteria

• skills/aeon/ ships SKILL.md, README.md, .plugin/plugin.json, and the .claude-plugin / .codex-plugin vendor symlinks.
• The skill is registered in marketplaces/openhands-extensions.json under category integrations, with no defaultEnabled (opt-in only).
• skills/index.js and the README catalog are regenerated deterministically (node scripts/build-skills-catalog.mjs yields no further diff).
• python scripts/sync_extensions.py --check reports the extensions in sync.
• uv run --group test pytest tests/test_skills_have_readme.py tests/test_skills_catalog.py tests/test_skill_plugin_loading.py -q passes.

Compare existing integration skills under skills/ and their entries in marketplaces/openhands-extensions.json, then use them as the pattern for skills/aeon/ and its vendor symlinks. Run node scripts/build-skills-catalog.mjs and python scripts/sync_extensions.py --check, followed by the three specified pytest targets. Done means the Aeon skill files, opt-in registry entry, generated catalogs, and sync checks all satisfy the acceptance criteria.