fix: keep MCP stdio clean in specmatic-node

[vedubhat]

Reason for change

• npx -y specmatic mcp server was failing during MCP initialization with a JSON parse error.
• The root cause was the Node wrapper capturing Java stdout/stderr and re-emitting them through its own output, which mixed logs into the MCP protocol stream.

What changed

• Special-cased mcp server in specmatic-node.
• Spawned the JVM process with stdio: 'inherit' for this command.
• Added regression coverage for:
  • the direct mcp server path
  • mcp server with a leading root flag such as --verbose