fix: PDF parsing broken after pnpm migration (#551)

- Pin officeparser to 5.0.0 which has internal pdfjs build
- pnpm resolved to 5.2.2 which uses external pdfjs-dist requiring DOMMatrix
- Remove @napi-rs/canvas override (no longer needed)
- Move canvas-confetti to devDependencies
- Add explicit error for legacy Office formats (.doc/.xls/.ppt)
- Update file picker to show supported formats based on parser type