fix(tui): preserve modified enter in plan questions

[fcoury-oai]

Why

Plan mode questionnaires reuse the shared composer for free-form answers, but the surrounding request_user_input overlay still treated every KeyCode::Enter as “advance to the next question.” That made Shift+Enter insert a newline in the composer and then immediately advance the questionnaire anyway.

Fixes #23448.

What Changed

• pass the live RuntimeKeymap into RequestUserInputOverlay so its embedded composer honors existing /keymap composer/editor remaps
• advance free-form questions only on the configured composer submit binding, instead of any Enter-shaped key event
• add regressions for Shift+Enter newline behavior and configured composer submit bindings inside the questionnaire UI

How to Test

1. Start Codex in Plan mode and trigger a request_user_input questionnaire with a free-form answer field.
2. Focus the free-form field, type a line, then press Shift+Enter.
3. Confirm the answer gains a newline and the questionnaire stays on the same question.
4. Press the configured submit binding, or plain Enter with the default keymap, and confirm the questionnaire advances as before.

Targeted tests:

• cargo test -p codex-tui bottom_pane::request_user_input::tests::freeform_ -- --nocapture

Notes

• cargo test -p codex-tui still reaches an unrelated existing stack overflow in app::tests::discard_side_thread_removes_agent_navigation_entry on this checkout.
• just argument-comment-lint is locally blocked by Bazel analysis failing in external compiler-rt before the lint runs.

[chatgpt-codex-connector]

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[canvrno-oai]

Tested with /plan mode and triggering a free form (Tab/Add notes) input. Shift+Enter added a newline as expected without attempting to submit the partial entry. Compared against the current release, where the issue was easily duplicated following the same steps.