fix: address flakiness in thread_resume_rejoins_running_thread_even_with_override_mismatch

[bolinfest]

Why

thread/resume responses for already-running threads can be reported as Idle even while a turn is still in progress. This is caused by a timing window where the runtime watch state has not yet observed the running-thread transition, so API clients can receive stale status information at resume time.

Possibly related: #11786

What

• Add a shared status normalization helper, resolve_thread_status, in codex-rs/app-server/src/thread_status.rs that resolves Idle/NotLoaded to Active { active_flags: [] } when an in-progress turn is known.
• Reuse this helper across thread response paths in codex-rs/app-server/src/codex_message_processor.rs (including thread/start, thread/unarchive, thread/read, thread/resume, thread/fork, and review/thread-started notification responses).
• In handle_pending_thread_resume_request, use both the in-memory active_turn_snapshot and the resumed rollout turns to decide whether a turn is in progress before resolving thread status for the response.
• Extend thread_status tests to validate the new status-resolution behavior directly.

Verification

• cargo test -p codex-app-server suite::v2::thread_resume::thread_resume_rejoins_running_thread_even_with_override_mismatch