French (fr) UI localization (#1224)

Adds a French catalog as a partial locale (missing strings fall back to English, like Russian), registered in the language list, with tests and attribution.

crates/ui-egui/src/i18n_ui_tests.rs

@@ -65,6 +65,7 @@ fn window_chrome_renders_in_the_active_language() {
         ("de", "BROWSER", "Auswahlfilter", "Flächen"),
         ("ko", "브라우저", "선택 필터", "면"),
         ("ru", "БРАУЗЕР", "Фильтр выделения", "Грани"),
+        ("fr", "NAVIGATEUR", "Filtre de sélection", "Faces"),
     ] {
         let mut h = Harness::new();
         h.app.preferences.language = lang.into();