Add plannotator plugin to docs

[backnotprop]

Plans are becoming first-class artifacts in agent workflows, but review and collaboration around them still feels ad hoc;

What this plugin does

Plannotator hooks into plan mode, submits a plan and opens an interactive UI, feedback is automated back to opencode - approval launches opencode into build mode. Local-first, no backend and explicit annotation.

Plannotator is something i just built 2 days ago. But seeing a lot of cool capability potential.

The plugin works better than cc hooks, as i can automatically launch opencode into build.

https://github.com/backnotprop/plannotator/tree/main/apps/opencode-plugin