add WguiFontSystem, remove FONT_SYSTEM singleton, custom fonts, add Light font weight

there are a few gzip-compressed ttf as for now, looks like variable fonts aren't parsed properly by cosmic_text. Not sure why. Also, we probably need to have a fallback for CJK characters in the future, or just fallback to the built-in ones in the OS.

wgui/src/i18n.rs

@@ -75,7 +75,7 @@ impl I18n {
 		log::info!("Guessed system language: {lang}");
 
 		match lang.as_str() {
-			"en" | "pl" | "it" | "ja" | "es" => {}
+			"en" | "pl" | "it" | "ja" | "es" | "de" => {}
 			_ => {
 				log::warn!("Unsupported language \"{}\", defaulting to \"en\".", lang.as_str());