feat: add device-side subtitle overlay using FreeType for rendering Chinese text

- Updated Cargo.toml to include freetype-rs for font rendering.
- Modified message.rs to introduce a new Message variant for subtitles.
- Enhanced HttpPlugin to send subtitle messages to the live2d plugin.
- Implemented text rendering in the live2d plugin using FreeType for Chinese characters.
- Added OpenGL shaders for rendering text overlays.
- Created a new text.rs module for handling text rasterization and texture rendering.
- Updated renderer.rs to integrate subtitle rendering logic.

Cargo.toml

@@ -40,3 +40,5 @@ semver = "1"
 
 # Live2D 渲染
 image = { version = "0.25", default-features = false, features = ["png"] }
+# 设备端字幕（中文光栅化，调用系统 FreeType 高级封装）
+freetype-rs = "0.13"