AI Router Proxy
===================
Proxy system for OpenRouter with prompt caching and app tracking.

Endpoints:
  - POST /app/:appName/session/:cacheKey/v1/chat/completions
    Dynamic session attribution route with sticky routing and prompt caching.
    Parameters:
      * appName: Application identifier
      * cacheKey: Sticky session / prompt cache key

  - POST /v1/chat/completions
    Fallback pass-through route with stable default session ID.

  - GET /
    This documentation endpoint.

Authorization:
  Requires 'Authorization: Bearer <your_api_key>' header.

Example Curl:
  curl -X POST https://router.syu.nl.eu.org/app/my-app/session/session123/v1/chat/completions \
    -H "Authorization: Bearer <your_api_key>" \
    -H "Content-Type: application/json" \
    -d '{"model": "openai/gpt-4o", "messages": [{"role": "user", "content": "Hello"}]}'