feat(i18n): update translations and improve error handling messages

- Updated site tagline and footer description in multiple languages.
- Enhanced error messages for various scenarios in the API service.
- Added translations for new error codes related to AI features and PDF processing.
- Improved user feedback in the UI components by utilizing i18n for dynamic text.
- Refactored error handling in the API service to map backend error codes to user-friendly messages.

frontend/package.json

@@ -12,7 +12,9 @@
     "preview": "vite preview",
     "lint": "eslint .",
     "test": "vitest run",
-    "seo:generate": "node scripts/merge-keywords.mjs && node scripts/generate-seo-assets.mjs"
+    "seo:generate": "node scripts/merge-keywords.mjs && node scripts/generate-seo-assets.mjs",
+    "lint:i18n": "node scripts/check-i18n-keys.mjs",
+    "lint:hardcoded": "node scripts/check-hardcoded-text.mjs"
   },
   "dependencies": {
     "@microsoft/clarity": "^1.0.2",