* style: update subtitle text shadow, JLPT underlines, and frequency topX
- Replace directional text-shadow with 4-corner outline shadow for sharper readability
- Increase JLPT level border-bottom from 2px to 3px; add drop-shadow filter
- Add margin-left 0.18em to character image token
- Raise frequencyDictionary topX default from 1000 to 10000
* docs: add subtitle style changelog fragment
* docs: update generated config examples
* style: wrap long textShadow strings and add blank line in CSS
