Remove AI marks

Multi-vendor anti-detection hygiene for text (Unicode + statistical rewrite) and files (C2PA / AI metadata across common containers).

Read if needed:

• references/mark-classes.md — Unicode / sampling / C2PA / containers
• references/vendor-notes.md — Claude, ChatGPT, Gemini/SynthID, Cursor, Midjourney, open-LLM
• references/removal-matrix.md — which layer when
• references/ethics.md — intended use
• references/how-claude-marks.md — Anthropic-specific detail
• references/markdiffusion.md — optional MarkDiffusion image harness (schemes, honesty caveats)

Setup: none

The cleaning scripts ship inside this skill, under scripts/. They are Python standard library only: no pip install, no virtualenv, no server, no Docker. Any python3 on PATH runs them.