feat: enhance custom font upload with WebView rendering, WOFF/WOFF2 support, preview & deletion

- Fix core bug: custom fonts now actually render in article WebView via
  @font-face injection and Jaguar local server font serving route
- Also fix built-in fonts (OpenSans/Roboto/SourceSerif) not rendering in WebView
- Add WOFF/WOFF2 format support for font upload
- Add font preview text in font picker and selected font indicator
- Add custom font deletion UI with confirmation dialog
- Add font file size validation (1KB-50MB)
- Update CSP to allow font-src from local server
- Add missing i18n translations for all 9 locales (zh, de, es, fr, hr, pt, tr, uk)
- Update Android build configuration and dependencies