chore: ignore generated iterator artifacts

[sit-d]

Summary

• add a repository .gitignore for the local Win32 build outputs documented in the README
• ignore runtime state/ MRU files and exports/ tables that the app creates beside the executable
• clarify that repository hygiene files are part of the shareable source set while generated runtime/export artifacts remain local by default

Verification

• git check-ignore --no-index -v iterator_gdi.exe iterator_gdi.obj iterator_gdi.pdb iterator_gdi.ilk state/session.mru exports/stable_logistic_R_q0_16.csv .vs/Iterator.suo local.user Thumbs.db
• verified tracked source/documentation files are not ignored with git check-ignore -q
• checked README/docs local Markdown links with a small Python script; README.md -> docs/usage.md resolves

Notes / Limitations

• This is a repository-hygiene/documentation change only; I did not attempt a Windows GDI build from this Linux cron environment.