Diacritics, tone styles, input methods

🔤 Vietnamese Text Toolkit

Six Vietnamese text chores in one box: strip diacritics for slugs, switch old ↔ new tone placement, turn raw Telex/VNI keystrokes into proper text, fix UPPER/lower/Title case, normalize Unicode to NFC.

Telex/VNI modes simulate an input method word by word (double the modifier key to escape it: 'ss' → literal s), so English words in the middle will get mangled — that's how IMEs work. Tone-style switching only touches the ambiguous pairs oa, oe, uy and leaves qu/gi words alone.