fix(taxi): keep target selection connected during flight

[Mathih13]

Selecting or clearing a target during a taxi flight ended the World Session. Argus recorded gw_set_target reducer failed: PLAYER_IN_TAXI_FLIGHT twice on October 10 at 22:19:48 and 22:21:13 UTC. The Standalone journal records the same reducer outcomes.

Allow target selection during flight. Keep Operator authorization, SessionActor ownership and the Transfer fence. CMaNGOS Classic permits this selection.

Refs #676. The logged cause is fixed here. Keep the issue open for its attended imported-route and reconnect check.

What you verified

• The encrypted Headless Client regression uses the real Gateway, Coordinator and a private Module instance. Before the fix, selection reset the connection. After the fix, selection and clearing each receive PONG and update the durable target. Flight state and money stay unchanged.
• The existing benilla_durable_ CI group includes the new regression.
• Module unit tests: 1,564 passed. Gateway suite: 2,145 passed, 31 ignored. The new durable regression ran separately and passed.
• Durable taxi Refusal contracts: 1 passed. Formatting and workspace Clippy pass.
• Two read-only adversarial reviews, GPT-6 Astra for standards and Claude Opus 5.5 for the issue requirements, found no code blocker. Both retained the attended-check limit below.

What you did NOT verify

No production update or attended build-5875 client test. Complete imported-route travel, landing presentation and reconnect without another fare remain to be checked. The checkout reflog identifies 839643e2 before the incident; it does not prove the running artifact at that time.

The production change is limited to one Module Gateway Verb. No schema or packet layout changes.

Model: GPT-6 Astra. Harness: Codex in T3 Code.