feat(web): unify fonts and refine viewcube

Preload one language-aware font resource across the interface, drawing text, and navigation labels.\n\nRender the navigation cube, ring, outlines, and labels through a 4x MSAA target.

src/i18n.rs

@@ -122,6 +122,7 @@ fn load_language(
     if requested.is_empty() {
         requested.push(loader.fallback_language().clone());
     }
+    #[allow(unused_variables)]
     let selected = i18n_embed::select(loader, &Localizations, &requested)?;
     #[cfg(target_arch = "wasm32")]
     if let Some(language) = selected.first() {
@@ -155,6 +156,16 @@ pub fn set_language(language: Language) -> Result<(), i18n_embed::I18nEmbedError
     load_language(loader(), language)
 }
 
+#[cfg(target_arch = "wasm32")]
+pub fn active_language_tag() -> String {
+    loader()
+        .current_languages()
+        .into_iter()
+        .next()
+        .unwrap_or_else(|| loader().fallback_language().clone())
+        .to_string()
+}
+
 /// Translate an application-facing source label from the complete UI catalog.
 ///
 /// Stable semantic ids remain preferable for new code. This compatibility