Fix queued messages during /review (#9122)

Sending a message during /review interrupts the review, whereas during
normal operation, sending a message while the agent is running will
queue the message. This is unexpected behavior, and since /review
usually takes a while, it takes away a potentially useful operation.

Summary
- Treat review mode as an active task for message queuing so inputs
don’t inject into the running review turn.
- Prevents user submissions from rendering immediately in the transcript
while the review continues streaming.
- Keeps review UX consistent with normal “task running” behavior and
avoids accidental interrupt/replacement.

Notes
- This change only affects UI queuing logic; core review flow and task
lifecycle remain unchanged.

codex-rs/tui/src/chatwidget/snapshots/codex_tui__chatwidget__tests__review_queues_user_messages_snapshot.snap

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+source: tui/src/chatwidget/tests.rs
+assertion_line: 3840
+expression: term.backend().vt100().screen().contents()
+---
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+• Working (0s • esc to interrupt)
+  ↳ Queued while /review is running.
+    ⌥ + ↑ edit
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+› Ask Codex to do anything
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+  100% context left · ? for shortcuts