feat: add reverse proxy support with configurable base path and trust proxy settings

[sonarta]

Description

This PR adds comprehensive reverse proxy support to enable deployment behind Kong, Nginx, or other load balancers with configurable base paths.

Changes Made

• Added new environment variables:

  • BASE_PATH: Configurable base path for mounting routes (e.g., /api/v1/whatsapp)
  • TRUST_PROXY: Enable trust proxy for proper IP forwarding behind reverse proxies

• Enhanced Express app configuration:

  • Routes now mount with configurable base path instead of hardcoded root (/)
  • Trust proxy setting for accurate client IP detection

• Improved WebSocket handling:

  • WebSocket upgrade handler now supports base path routing
  • Uses X-Forwarded-Host header for proper host detection behind proxies

• Fixed rate limiting:

  • Rate limiter now uses real client IP instead of proxy IP
  • Proper IP extraction when behind reverse proxy

• Updated configuration:

  • Added new environment variables to .env.example
  • Comprehensive documentation in REVERSE_PROXY_SETUP.md

Testing

• Tested with Kong API Gateway configuration
• Verified WebSocket connections work with base path
• Confirmed rate limiting uses correct client IPs
• All existing functionality remains unchanged when new variables are not set

Documentation

• Created REVERSE_PROXY_SETUP.md with Kong, Nginx, and Docker Compose examples
• Updated .env.example with new configuration options
• Includes troubleshooting guide for common reverse proxy issues

Backward Compatibility

✅ Fully backward compatible - existing deployments continue to work without any changes

Related Issues

Fixes issues with:

• 404 errors when deployed behind reverse proxy with path prefix
• WebSocket connection failures in proxy environments
• Incorrect rate limiting when all requests appear from proxy IP