feat(iconv): support `//translit` transliteration mode

[chaliy]

Summary

iconv -f utf-8 -t ascii//translit fails silently — the //translit suffix on the target encoding is not supported.

Reproduction

echo "Héllo Wörld" | iconv -f utf-8 -t ascii//translit
# Expected: "Hello World" (accents transliterated to ASCII)
# Actual: empty output or error

Context

Discovered while running bashblog via bashkit CLI. Bashblog uses iconv with //translit in its filename conversion pipeline to strip diacritics from post titles:

convert_filename="iconv -f utf-8 -t ascii//translit | sed 's/^-*//' | tr [:upper:] [:lower:] | tr ' ' '-' | tr -dc '[:alnum:]-'"

Without //translit, non-ASCII characters in blog post titles produce empty or broken filenames.

Expected behavior

iconv -f utf-8 -t ascii//translit should transliterate non-ASCII characters to their closest ASCII equivalents (e.g., é → e, ö → o).