ci(publish-mcp): simplify login command usage

Author: masnwilliams

.github/workflows/publish-mcp.yml

@@ -38,8 +38,7 @@ jobs:
       
       - name: Login to MCP Registry
         run: |
-          echo "${{ secrets.MCP_PRIVATE_KEY }}" > key.pem
-          ./mcp-publisher login dns --domain onkernel.com --private-key-file key.pem
+          ./mcp-publisher login dns -domain onkernel.com -private-key "${{ secrets.MCP_PRIVATE_KEY }}"
       
       - name: Publish to MCP Registry
         run: ./mcp-publisher publish