Implemented discovery logic already exists in tests/forms_integration.rs:
- discover_pdf_fixtures() uses walkdir for recursive PDF discovery
- find_pdf_fixtures() uses std::fs for non-recursive discovery
- All 6 tests pass, including test_discover_pdf_fixtures which prints discovered fixtures
- Test is idempotent with no side effects
Acceptance criteria:
✅ Discovers PDF files in tests/fixtures/forms/
✅ Prints discovered fixtures for verification
✅ cargo test forms_integration passes (6/6 tests)
✅ Test runs identically on repeated execution
Verification: notes/bf-14tjh.md
