fix(tui): clarify footer shortcut overlay hints

[fcoury-oai]

Why

The TUI shortcut overlay used static labels for Tab and Ctrl+C, even though both keys change behavior while a task is running. That made the visible help misleading: idle Tab submits rather than queues, and active-turn Ctrl+C interrupts rather than exits.

Closes #25531.
Closes #25564.

What Changed

• Pass task-running state into the shortcut overlay renderer.
• Render Tab as submit message while idle and queue message while work is running.
• Render Ctrl+C as exit while idle and interrupt while work is running.
• Add snapshot coverage for the active-work shortcut overlay and update idle overlay snapshots.

How to Test

1. Start Codex and open the shortcut overlay with ? while no task is running.
2. Confirm the overlay shows tab to submit message and ctrl + c to exit.
3. Start a task, then open or keep the shortcut overlay visible while work is running.
4. Confirm the overlay shows tab to queue message and ctrl + c to interrupt.
5. Type a follow-up prompt during active work and press Tab; confirm it queues rather than submitting immediately.

Targeted tests:

• just test -p codex-tui footer_snapshots
• just test -p codex-tui footer_mode_snapshots

Validation Notes

just test -p codex-tui currently has two unrelated guardian feature-flag test failures on this base:

• app::tests::update_feature_flags_disabling_guardian_clears_manual_review_policy_without_history
• app::tests::update_feature_flags_disabling_guardian_clears_review_policy_and_restores_default

just argument-comment-lint codex-rs/tui/src/bottom_pane/footer.rs could not run locally because the prebuilt wrapper requires dotslash; the touched Rust diff was manually inspected for opaque positional literals.

[fcoury-oai]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: a8af949784

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[fcoury-oai]

@codex review

[chatgpt-codex-connector]

Codex Review: Didn't find any major issues. You're on a roll.

ℹ️ About Codex in GitHub

Your team has set up Codex to review pull requests in this repo. Reviews are triggered when you

• Open a pull request for review
• Mark a draft as ready
• Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

Codex can also answer questions or update the PR. Try commenting "@codex address that feedback".

[etraut-openai]

Looks good