Remove Vietnamese diacritics

When to strip diacritics

• URL slugs: many systems mishandle non-ASCII URLs. The slug generator additionally handles whitespace & punctuation.
• Filenames: avoid encoding bugs when syncing across Windows / macOS / Linux.
• Usernames, emails, code identifiers: legacy systems often accept ASCII only.
• Fuzzy search: a diacritic-free index lets users find results even when they type without tone marks.

How it works

This tool uses String.prototype.normalize('NFD') to split characters into a base + combining mark, then removes the marks. The optional đ → d conversion is handled separately because đ is a base character, not a combination.