Address code review feedback from cubic-dev-ai:
P1: Unconditionally passing CJKmainfont broke non-CJK conversions in
environments without CJK fonts. Now the source file is scanned for CJK
characters and the font argument is only added when CJK content is
detected.
P2: Hardcoded Noto Sans CJK SC only covers Simplified Chinese. Now
detects the specific CJK language (Japanese Kana, Korean Hangul, or
Chinese Hanzi) and selects the appropriate font variant (JP/KR/SC).
Changes:
- Add detectCJKFont() that reads the source file and returns the
correct Noto Sans CJK variant, or null for non-CJK content
- CJK font argument is only added when detectCJKFont returns non-null
- Detection order: Japanese (Kana) > Korean (Hangul) > Chinese (Hanzi)
since Japanese also uses Kanji shared with Chinese
- Graceful fallback: if file can't be read, no CJK font is added
- Update tests to use temp files with real CJK content (11 tests total)
0abd934046