feat: Add German translation support for MinIO WebUI

- Set up i18n infrastructure with react-i18next
- Add German as default language with English fallback
- Create comprehensive translation files for all UI components
- Translate Dashboard, QuickStartWizard, Reports, and navigation
- Add language switcher in app header
- Maintain existing German email template in backend
- Create modular translation structure with namespaces
- Add testing checklist and implementation summary

All user-facing strings in dashboard, quick wizard, and reports
sections are now available in German, fulfilling the requirement
for complete German localization.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/package.json

@@ -16,10 +16,13 @@
     "axios": "^1.6.5",
     "chart.js": "^4.4.1",
     "date-fns": "^3.2.0",
+    "i18next": "^25.3.2",
+    "i18next-browser-languagedetector": "^8.2.0",
     "react": "^18.2.0",
     "react-chartjs-2": "^5.2.0",
     "react-dom": "^18.2.0",
     "react-hook-form": "^7.48.2",
+    "react-i18next": "^15.6.1",
     "react-router-dom": "^6.21.1",
     "react-scripts": "5.0.1",
     "typescript": "^5.3.3",