- Add test_extract_all_discovered_pdfs() function to forms_integration.rs
- Use walkdir-based discover_pdf_fixtures() for recursive PDF discovery
- Spawn pdftract extract --json process for each PDF and capture output
- Print detailed status and output preview for debugging
- Fix pdftract_bin() path resolution (workspace target dir)
Closes bf-394lb. Verification: notes/bf-394lb.md. Tests: PASS (compiles, runs, no hangs).
