test: Switch from docker SDK to gradio SDK 6.0.0 to verify MCP pin fix

HuggingFace team confirmed that the MCP version pinning issue affecting
Gradio SDK spaces with MCP is resolved. Testing the fix by:

Changes:
- sdk: docker → gradio
- Added sdk_version: 6.0.0
- Removed app_port (not needed for gradio SDK)

Keeping Dockerfile in place for easy rollback if needed. This is a quick
test to confirm the fix works and provide feedback to the Gradio team.

README.md

@@ -3,8 +3,8 @@ title: TraceMind MCP Server
 emoji: 🤖
 colorFrom: blue
 colorTo: purple
-sdk: docker
-app_port: 7860
+sdk: gradio
+sdk_version: 6.0.0
 pinned: true
 license: agpl-3.0
 short_description: MCP server for agent evaluation with Gemini 2.5 Flash