revert: Switch back to docker SDK - gradio SDK 6.0.0 test failed

The gradio SDK 6.0.0 test did not work as expected. Reverting to docker SDK
configuration that was working previously.

Changes:
- sdk: gradio → docker
- Removed sdk_version: 6.0.0
- Added back app_port: 7860

Will report to Gradio team that the MCP pinning issue persists even after
their reported fix.

README.md

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