feature: localization (#32)

* build: add nlohmann/json library

* build(deps): add harfbuzz dependency

* feat(cmake): add guard to reject macOS builds

* feat(font): add HarfBuzz shaping and replace font with unifont

* feat(localization): add i18n support with en_US and zh_CN translations

Implement Localization class to load JSON translation files. Replace hardcoded strings in UI with translation keys and update sliders/combo buttons to use dynamic text.

* feat(localization): detect system locale for language default

* feat(settings): add language selection option with restart notification

* fix: use vckpg to add freetype on windows

src/render/renderer.cpp

@@ -187,7 +187,7 @@ void Renderer::render_lable(const Label& label) {
 
     shader.set_loc("projection", m_ui_proj_matrix);
 
-    Font::text_texture()->bind(0);
+    Font::get().text_texture()->bind(0);
     auto& data = label.data();
     auto pos = label.pos();
     auto& text_style = label.text_style();