Use pnpm instead of npx and add --unsafe flag for Biome
- Changed from npx to pnpm biome in lefthook.yml (project uses pnpm)
- Added --unsafe flag to apply safe fixes as per Biome official docs
- Configured pnpm to only build lefthook dependency (not other deps)
Co-authored-by: yuki-takei <1638767+yuki-takei@users.noreply.github.com>