[FEAT] LiveSmoke : env-gated live bridge test (UNITY_MCP_LIVE=1 npm run test:live)

- Runs the modified server against a REAL Unity editor, read-only calls only
- Validates the new-server / old-plugin version-skew direction users actually hit
- Verified live against POC Tranverser Fantome (Unity 6000.3.9f1, plugin 2.27.0): discovery, editor_state, console_log, compact default, stdout purity - 5/5