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/pt.json

@@ -101,12 +101,12 @@
   "AppearanceSettings": {
     "sectionTitle": "Aparência do tema",
     "sectionDescription": "Escolha claro, escuro ou seguir o sistema. As configurações são salvas automaticamente.",
-    "themeMode": "Modo do tema",
-    "placeholder": "Selecione o modo do tema",
+    "themeMode": "Modo de tema",
+    "placeholder": "Selecionar modo de tema",
     "system": "Seguir o sistema",
     "light": "Claro",
     "dark": "Escuro",
-    "currentTheme": "Tema atualmente em uso: {theme}",
+    "currentTheme": "Tema efetivo atual: {theme}",
     "resolvedTheme": {
       "light": "Claro",
       "dark": "Escuro",