feat: add aeon skill to the extensions registry

[aaronjmars]

• A human has tested these changes.

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Why

Aeon (github.com/aeonfun/aeon) is an open-source framework that runs a user's own skills on a schedule in GitHub Actions. There is no skill in this registry for operating an Aeon instance, so an agent working in one has no guidance. This adds one, in the same shape as the other integration skills here.

Summary

• Add skills/aeon: SKILL.md (the operator playbook), README.md, .plugin/plugin.json, and the .claude-plugin / .codex-plugin vendor symlinks.
• Register it in marketplaces/openhands-extensions.json under category "integrations".
• Regenerate skills/index.js and the README catalog with the repo's own scripts.

Issue Number

Fixes #515

How to Test

From the repo root:

• python scripts/sync_extensions.py --check - extensions report in sync.
• node scripts/build-skills-catalog.mjs - skills/index.js regenerates with no further diff (deterministic).
• uv run --group test pytest tests/test_skills_have_readme.py tests/test_skills_catalog.py tests/test_skill_plugin_loading.py -q - README, catalog, and plugin-manifest checks pass.

The skill itself operates a live Aeon instance through its ./aeon CLI and gh; exercising that is out of scope for this registry's tests.

Video/Screenshots

N/A - a Markdown skill definition plus a marketplace entry, no UI.

Notes

• category is "integrations"; no defaultEnabled, so it stays off unless a user opts in.
• I maintain the Aeon project (github.com/aeonfun/aeon); plugin.json credits Aeon Inc and points homepage/repository at the project.

[all-hands-bot]

👋 This PR needs a couple of things fixed before OpenHands can review it:

• the PR description's HUMAN: section needs at least 20 characters describing what you tested, not just the template placeholder

Push an update once this is addressed and this check re-runs automatically.

This is an automated check - no AI was used to generate this comment.

[aaronjmars]

Maintainer heads-up: the Validate PR description check is red only because #515 (which I opened for this addition) has no ready-for-dev label yet, and that label is repo-managed so I can't set it on a fork PR. Could a maintainer apply ready-for-dev to #515? The check re-runs and passes automatically once it's labeled. Everything else on the PR is green and it's a self-contained registry addition. Thanks!