feat: add danmuku plugin documentation and i18n setup guide

- Created a new documentation file for the danmuku plugin with code examples.
- Added comprehensive language settings documentation, including default languages, import instructions, and examples for adding and modifying languages.
- Updated the i18n documentation to reflect changes in language handling and provide clear examples for users.

CHANGELOG.md

@@ -13,6 +13,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Add `artplayer-plugin-jassub` plugin
 - Add `artplayer-proxy-mediabunny` plugin
 - Add `artplayer-plugin-audio-track` plugin
+- Deprecate `artplayer-plugin-libass` plugin
 
 ## [5.3.0] - 2025-09-06