Add invoice fixture with ground truth text for OCR testing.
Files:
- tests/fixtures/scanned/invoice/invoice-300dpi.pdf: 300 DPI scanned invoice
- tests/fixtures/scanned/invoice/invoice-300dpi-ground-truth.txt: complete text content
- tools/generate_invoice_pdf_fixtures.py: fixture generator script
- tests/fixtures/PROVENANCE.md: added provenance entries for new fixtures
- notes/bf-337i2.md: verification note
Verification:
- PDF is image-based (type=image, not text-embedded)
- Resolution: 300 DPI (x-ppi=300, y-ppi=300)
- Dimensions: 2550 x 3300 pixels (letter size at 300 DPI)
- Ground truth contains complete invoice text with headers, addresses, line items, totals
Closes bf-337i2
