Add enhanced debugging to diagnose Gamma API connectivity issues

[berlinbra]

This PR adds enhanced debugging to help diagnose why the Gamma API is failing and falling back to CLOB client with outdated data.

What this adds

1. API Connectivity Test on Startup

• Tests if the Gamma API is reachable when the server starts
• Shows a sample market if successful
• Clear error messages if it fails

2. Enhanced Debug Logging

• Logs response headers and status codes
• Shows raw response content (first 500 chars) for debugging
• Logs the first market returned as a sample
• More detailed error messages for different failure types

3. Better Fallback Handling

• Clear warning when falling back to CLOB client
• Indicates that CLOB data may be outdated
• Shows exactly why the Gamma API failed

How to use

1. Switch to the debug-gamma-api branch

2. Run the server: uv run src/polymarket_mcp/server.py

3. Look for the startup connectivity test:

   [DEBUG] Testing Gamma API connectivity...
   [DEBUG] ✅ Gamma API is reachable! Status: 200
   

   Or error messages if it fails

4. When calling list-markets, check the debug output to see:

   • What parameters are being sent
   • The API response status and headers
   • Raw response content
   • Whether it's falling back to CLOB

This should help identify whether the issue is:

• Network connectivity/blocking
• API authentication requirements
• Response format changes
• Rate limiting
• Or something else