i18n: add the Bulgarian (bg) catalog

The catalog holds the 4,789 rows the other complete catalogs hold: the whole
interface (every menu string and `tl!` literal) and the status and error
messages, in the Bulgarian vocabulary of vector illustration, following
Adobe Illustrator's Bulgarian conventions; one/other plural forms.

Clean-room from VectorCraft's English meaning, drafted with AI assistance
(Gemini); a native speaker has not reviewed it yet. `bg-BG` and every other
`bg-*` locale resolve here.

`cargo test -p vectorcraft-ui-egui i18n::tests` passes (46 tests, including
complete menu, literal, message and font coverage).

crates/ui-egui/src/i18n/mod.rs

@@ -94,7 +94,7 @@ fn plural_polish(n: u64) -> usize {
 }
 
 /// The registry. English first: it is the fallback and the source language.
-pub static LANGUAGES: [LangInfo; 16] = [
+pub static LANGUAGES: [LangInfo; 17] = [
     LangInfo { code: "en", name: "English", source: "", plural: plural_one_other, complete_menus: false, catalog: OnceLock::new() },
     // Japanese: the whole interface (every menu string and `tl!` literal) and the status and error
     // messages, keeping the product, workspace and perspective preset names in English (`MENU_KEEP_AS_IS`).
@@ -164,6 +164,16 @@ pub static LANGUAGES: [LangInfo; 16] = [
         complete_menus: true,
         catalog: OnceLock::new(),
     },
+    // Bulgarian: the whole interface (every menu string and `tl!` literal) and the status and error
+    // messages, with one/other plural forms; every `bg-*` locale (including `bg-BG`) resolves here.
+    LangInfo {
+        code: "bg",
+        name: "Български",
+        source: include_str!("bg.tsv"),
+        plural: plural_one_other,
+        complete_menus: true,
+        catalog: OnceLock::new(),
+    },
     // Hungarian: the whole interface and the status and error messages, keeping the same names in
     // English as Spanish; a count takes the singular ("3 réteg"), so plurals have one form. Every
     // `hu-*` locale (including `hu-HU`) resolves here.