docs(ecosystem): add AION time-series harness plugin

[ztxtech]

Adds AION to the Plugins section of the English ecosystem page (packages/web/src/content/docs/ecosystem.mdx).

AION is a time-series harness for OpenCode: a 4-layer (task / workspace / execution / review) multi-agent system with a governance hierarchy, 17 skills, 8 coordination protocols, and leakage prevention. Companion paper: arXiv:2605.25045.

Why only the English file?

I deliberately did not touch the 17 locale copies under packages/web/src/content/docs/<locale>/ecosystem.mdx. The repo's docs-locale-sync workflow (.github/workflows/docs-locale-sync.yml) auto-syncs locale docs whenever an English doc under packages/web/src/content/docs/*.mdx changes on dev, and its instructions explicitly say: "Do not modify English source docs in packages/web/src/content/docs/*.mdx" from inside the sync job. If I had pre-translated the locales, the bot would either conflict with my edits or undo them. Happy to pre-translate the 17 locale files in a follow-up commit if maintainers prefer that flow over the bot.

Checklist

• One change in one file (English ecosystem.mdx only)
• Repo is a public OpenCode plugin (compiles to a single self-contained .opencode/plugins/aion.js bundle)
• Plugin is actively maintained (4 releases, last release Jun 14 2026)
• Companion paper on arXiv

[github-actions]

This PR doesn't fully meet our contributing guidelines and PR template.

What needs to be fixed:

• PR description is missing required template sections. Please use the PR template.

Please edit this PR description to address the above within 2 hours, or it will be automatically closed.

If you believe this was flagged incorrectly, please let a maintainer know.

[github-actions]

This pull request has been automatically closed because it was not updated to meet our contributing guidelines within the 2-hour window.

Feel free to open a new pull request that follows our guidelines.