fix: emit one Queue terminal response

[smiggleworth]

Summary

• give Queue actor replies and ingress timeout replies a shared one-shot terminal-response claim
• preserve that claim for deferred long-poll receives
• suppress whichever response loses the race, preventing client FIFO corruption and duplicate delivery

Why

The hosted Destroyer Queue overload scenario exposed a real response-ordering race: a Queue command could complete just as the synchronous domain dispatch wait expired. Ingress emitted an indeterminate timeout and the actor later emitted the normal response for the same request. The extra frame shifted the client per-message-type FIFO, so a later accepted enqueue could appear retryably rejected and be sent again.

Failure evidence: https://github.com/cntryl/fitz-destroyer/actions/runs/33768148936/job/100691408320

Validation

• cargo fmt --all -- --check
• cargo test --workspace
• cargo clippy --locked --workspace --all-targets --all-features -- -D warnings -D clippy::pedantic
• cargo test api::runtime_ingress::tests::domain_backpressure
• cargo test domains::queue::sink

The regression was observed red before the dispatcher arbitration was added (two terminal responses) and green afterward (exactly one).