Add documentation explaining how _server_url() resolves the host
when Server.host is 0.0.0.0 or :: — using the default route
interface IP instead of hardcoding 127.0.0.1.
Added Transport Security section to MCP service documentation covering:
- Default behaviour (disabled, allow all hosts)
- How to enable protection via gns3_server.conf
- Protection mechanism (Host header validation)
- DNS rebinding attack prevention explanation
- Behaviour summary table
