sync-shadcn

# Sync Shadcn Read `docs/sync/shadcn/status.json` and `decisions.md` when present, the exact upstream local checkout and its revision, and the named Plate files. Bootstrap missing sync state from evidence; never invent a last-applied baseline. Planning is default. An explicit planning-only request stops at a reviewable plan. Existing implementation authority carries through readiness. Scope a named request to its range; an unscoped sync accounts for the complete range. Compare base, current upstream and local files. Classify each relevant hunk as upstream-only, local-only, equivalent, conflicting, renamed, deleted or unknown base. Preserve Plate-owned editor content, demos, registry, API MDX, Chinese docs, MCP, Plus hooks and analytics. Upstream owns its generic docs machinery. `status` reports freshness, accounted range and next work without mutation. `review` revalidates a plan against both current revisions. `dashboard` presents unresolved structured rows through the existing board script. `apply` changes only accepted rows after recomputing their classification. Keep target forks and named omissions explicit; no whole-file overwrite from title similarity. `parity` compares the real registry/install request, response, metadata and CLI behavior source by source. Prove declared dependency and alias behavior through an installed consumer. This checkout's authored registry metadata is the owner; do not assume an absent dependency-derivation builder. Record each source row, its Plate home, decision, proof and remaining gap. Advance the synced baseline only after every row in that range is accounted for and applicable checks pass. Partial slices retain the earlier baseline. Run `plate-docs` for public docs, `plate-ui` for copied UI, `verify` for routes and consumers, and `changeset` for registry release notes. CI owns registry build output. Downstream application UI sync belongs to `sync-plate-ui`.