style: update subtitle text shadow, JLPT underlines, and frequency topX default (#96)

* 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

src/renderer/subtitle-render.ts

@@ -89,7 +89,7 @@ function sanitizeSubtitleHoverTokenBackgroundColor(value: unknown): string {
 
 const DEFAULT_FREQUENCY_RENDER_SETTINGS: FrequencyRenderSettings = {
   enabled: false,
-  topX: 1000,
+  topX: 10000,
   mode: 'single',
   singleColor: '#f5a97f',
   bandedColors: ['#ed8796', '#f5a97f', '#f9e2af', '#8bd5ca', '#8aadf4'],