Apple runner: bound every runner phase by the request's absolute deadline #4023

Follow-up from #4017 (#3861).

Context. #4017 binds an absolute deadline only to the iOS launch-confirmation alert commands, and only at the last step before sending. That step comes after the readiness preflight in sendRunnerCommandAfterPreflight, through an opt-in RunnerCommand.deadline. The other runner phases still run on their own budgets, so a request can outlive its caller:

• runner startup and log preparation;
• the readiness preflight's own budget;
• the up-to-45 s exchange;
• read-only resends.

The runner also does not cancel work when HTTP disconnects (runner-exchange.ts).

Required behavior.

• A request's absolute deadline bounds every runner phase for any command that carries one.
• No phase starts after the deadline.
• A phase that is already running is capped at the time left.
• Expiry returns a typed failure, and keeps unknown-effect reporting for work that was already dispatched.

Out of scope. Changing the default budget of any command that has no deadline.