Add full language translation support and settings option

Integrates i18next and react-i18next for internationalization, adds German language support, and implements a language selection feature in the settings page.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: ceced2fc-aa46-458d-ba87-ddd4b7bb1518
Replit-Commit-Checkpoint-Type: intermediate_checkpoint
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/659922a9-0087-461c-90dd-6d9a58b81d4d/ceced2fc-aa46-458d-ba87-ddd4b7bb1518/un1X8jl

package.json

@@ -54,6 +54,7 @@
     "express": "^4.21.2",
     "express-session": "^1.18.1",
     "framer-motion": "^11.13.1",
+    "i18next": "^25.6.0",
     "input-otp": "^1.4.2",
     "lucide-react": "^0.453.0",
     "memorystore": "^1.6.7",
@@ -65,6 +66,7 @@
     "react-day-picker": "^8.10.1",
     "react-dom": "^18.3.1",
     "react-hook-form": "^7.55.0",
+    "react-i18next": "^16.1.6",
     "react-icons": "^5.4.0",
     "react-resizable-panels": "^2.1.7",
     "recharts": "^2.15.2",