GSD planning artifacts (.planning/**) are rewritten by tooling on every workflow
run and are never hand-formatted. Including them in Prettier scope caused
pnpm format:check to exit 1 on virtually every future PR, making the SC-3
green baseline impossible to hold. Add .planning/ to .prettierignore, mirroring
the same rationale as dist/ and apps/api/src/db/migrations/.
Real source docs (README.md, docs/**) remain in Prettier scope.
No playwright-report/, test-results/, or coverage/ directories exist to ignore.
Lucas Berger