Update docs and comments for jpeglib migration (v4.2.0)

- Replace jpegio references with jpeglib in comments/docstrings
- Update sanitize-for-image.sh to use system Python 3.11+ (no pyenv)
- Update rpi/patches/README.md for jpeglib world
- Add AUR build artifacts to .gitignore

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.gitignore

@@ -97,3 +97,8 @@ rpi/*.tar.zst.zip
 rpi/*.img
 rpi/*.img.zst
 rpi/*.img.zst.zip
+
+# AUR build artifacts
+aur-upload/
+aur/.SRCINFO
+aur/*.pkg.tar.zst