fix: use dynamic port in server scenario tests to avoid conflicts

[max-stytch]

Motivation and Context

• Server scenario tests were hardcoded to port 3001, which is a commonly used port. If anything is already running on it, the tests hang for 30s and then fail
• Replace TEST_PORT = 3001 with a getFreePort() helper that lets the OS assign a free port via listen(0). This is the same mechanism that all other invocations of listen() in the codebase already use.
• Tests pass consistently regardless of what else is running locally

How Has This Been Tested?

• All 87 tests pass locally (verified via pre-push hook)
• CI passes

Breaking Changes

Types of changes

• 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

[nbarbettini]

LGTM