ci: update MCP login to use DNS and key file

Author: masnwilliams

.github/workflows/publish-mcp.yml

@@ -37,7 +37,9 @@ jobs:
           chmod +x mcp-publisher
       
       - name: Login to MCP Registry
-        run: ./mcp-publisher login github-oidc
+        run: |
+          echo "${{ secrets.MCP_PRIVATE_KEY }}" > key.pem
+          mcp-publisher login dns --domain onkernel.com --private-key-file key.pem
       
       - name: Publish to MCP Registry
         run: ./mcp-publisher publish