fix(i18n): restore pre-existing AppearanceSettings translations

Task 7 inadvertently overwrote 18 carefully-tuned translations across 7 languages
(ar/de/es/fr/ja/ko/pt) with the plan author's slightly different wording while
adding the new themeColor / zoomLevel / resetToDefaults keys. The new additions
remain intact; only the pre-existing keys are reverted to the project's original
translations (e.g. de "Designmodus" instead of "Design-Modus", ja
"システム追従" instead of "システムに従う"). Affects: sectionDescription,
themeMode, placeholder, system, currentTheme.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/i18n/messages/fr.json

@@ -102,11 +102,11 @@
     "sectionTitle": "Apparence du thème",
     "sectionDescription": "Choisissez clair, sombre ou suivre le système. Les paramètres sont enregistrés automatiquement.",
     "themeMode": "Mode du thème",
-    "placeholder": "Sélectionnez le mode du thème",
+    "placeholder": "Sélectionner le mode du thème",
     "system": "Suivre le système",
     "light": "Clair",
     "dark": "Sombre",
-    "currentTheme": "Thème actuellement appliqué : {theme}",
+    "currentTheme": "Thème effectif actuel : {theme}",
     "resolvedTheme": {
       "light": "Clair",
       "dark": "Sombre",