Sync Plate UI

Handle $ARGUMENTS.

Goal: sync Plate UI registry components from this repo into a downstream app without flattening that app's product forks. The workflow reads Plate registry source, generated changelog JSON, and downstream local files; classifies upstream-owned versus target-owned hunks; writes reviewable artifacts; then applies only accepted sync rows.

This is not sync-shadcn. sync-shadcn compares upstream shadcn docs with Plate docs. sync-plate-ui compares Plate UI registry source with a target app that copied and customized Plate UI, such as ../potion.

This skill is consumer-side only. It reads generated Plate UI changelog JSON; it does not create upstream Plate changelog entries. Upstream Plate devs author those through the changeset skill and apps/www/src/registry/changelog/entries/*.mdx.