- update IMAGE_LIST.md and all slide files
- keep karlheinz-brandenburg.jpg and suzanne-vega.jpg as .jpg (real photos)
- keep code examples unchanged (exiftool, HTML examples)
- extract _frontmatter.md, _intro.md, _outro.md as shared components
- create separate files per termin with date-topic naming convention:
2025-12-19-termin-1-grundlagen-text-audio.md
2026-01-09-termin-2-bild-audio-video.md
2026-01-23-termin-3-speichermedien-schnittstellen.md
2026-01-30-termin-4-distribution-apis-zukunft.md
2026-xx-xx-termin-5-vertiefung-offene-fragen.md
- keep index.md.bak as backup (gitignored)