Fix errors when mounting to non-root directories.

[geekwish]

Fix errors when mounting MCP server to non-root directories.

Motivation and Context

When I mounted sse_app to a different directory using the method in the readme, I found that the path of the messages returned by sse was wrong. My patch fixes this problem.

How Has This Been Tested?

I tested the sse service in the n8n workflow and it works fine.

Breaking Changes

If the user mounts sse_app to a non-root directory, the user needs to modify the code and provide the real path.

Types of changes

• [x ] Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context