[CI] package-only PRs skip docs/playground build checks

[johnleider]

Summary

A PR that touches only packages/** (e.g. renaming/removing an export, changing a prop type) can break docs examples or playground usage and still pass every PR gate. The breakage surfaces only post-merge as a failed deploy.

Location

• package.json:27 typecheck and package.json:9 build are --filter=./packages/* only; the always-run PR build job (.github/workflows/pr-checks.yml:63-70) builds packages only.
• pr-checks.yml:81-98 dorny/paths-filter gates docs-check / playground-check on apps/docs/** / apps/playground/** — so a packages/**-only PR skips both.
• Vitest is colocated in packages/0/src (examples aren't tested). docs-deploy.yml / playground-deploy.yml run only on push to master (post-merge).

Impact

CI/DX hygiene, not runtime/security. Coolify keeps serving the last good image, so a failed deploy stalls the update rather than taking the site offline; cost is red CI on master + a fix-forward. Note: vite-ssg build does not type-check, so type-level example breakage is caught nowhere — the path-filter fix below catches removed/renamed exports (the common case).

Suggested fix

Add - 'packages/**' to both the docs and playground filter lists in pr-checks.yml (~:95-98). This reuses the existing docs-check / playground-check jobs (which run build:docs / build:play), only paying the build cost when packages or the respective app actually change.