[Issue] Add proper support for Japanese spacing

[allenwang28]

For Anki usage, we use {kanji}[{hiragana}] for furigana. We need a space before the kanji so it displays properly in Anki.

We currently rely on GPT to properly space for furigana is inconsistent, leading to the need for manual edits. We could automate this with the right tooling, we just need to set this up