When kuromoji marks a katakana token as reading '*' (unknown word — common
for band names like ヨルシカ), the code fell back to the surface_form which
is still katakana. _hiraToRomaji can't handle katakana so it passed through
unchanged, causing sort tags to show ヨルシカ instead of Yorushika.
Fix: if the surface_form contains katakana and reading is *, convert it
mechanically via _kataToHira + _hiraToRomaji — katakana-to-romaji is always
unambiguous and needs no dictionary.
Also add a Japanese-char guard in the frontend when applying romaji index
values, so stale cache entries can never overwrite correct values with Japanese.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>