feat: Add i18n with 7 languages (DE, EN, ES, FR, AR, RU, PL)

- Added vue-i18n with language switcher in header
- Flag icons with language codes dropdown
- RTL support for Arabic
- Translated all navigation, auth, and module labels
- Language preference saved to localStorage

package.json

@@ -13,6 +13,7 @@
     "@vueuse/core": "^10.7.0",
     "pinia": "^2.1.0",
     "vue": "^3.4.0",
+    "vue-i18n": "^9.14.5",
     "vue-router": "^4.3.0"
   },
   "devDependencies": {