docs: add Copilot usage and quota viewer plugins to ecosystem docs

[fitri]

Issue for this PR

Closes #35768

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

Adds my plugin, Copilot Quota for OpenCode, to the Plugins table in the ecosystem docs.

Its a TUI plugin that shows live GitHub Copilot usage in the right sidebar, next to Context and LSP: your plan, a used/remaining bar, premium interactions used vs. entitlement, and the days until reset. It reuses the Copilot OAuth token OpenCode already stores after /connect, so there is no extra setup — no PAT, no org config. It calls the same internal endpoint the official Copilot editors use (copilot_internal/user), which is unversioned, so the widget falls back to a plain status message if that endpoint ever changes shape instead of crashing.

Repo: https://github.com/fitri/opencode-copilot-usage-plugin

How did you verify your code works?

Ran it against my own OpenCode setup with a live Copilot Business account. Confirmed the sidebar renders inside an open session (plan, bar, premium usage, reset countdown), updates after each assistant response, and that tsc passes with no errors.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

[alicansag]

Cannot access the repo, is it private?

[fitri]

Cannot access the repo, is it private?

Sorry, changed the repo to public

[fitri]

Updated with screenshot of the plugin