feat(tui): make turn interruption keybind configurable (#24766)

## Why

Interrupting an active turn is currently fixed to `Esc`, which is easy
to hit accidentally and cannot be customized through `/keymap`. This
gives users a less accidental binding while preserving the existing
default.

## What Changed

- Adds `tui.keymap.chat.interrupt_turn` to `/keymap`, defaulting to
`esc` and supporting remapping or unbinding.
- Uses the configured interrupt binding for running-turn status, queued
steer interruption, and `request_user_input`, including the visible
hints.
- Preserves local `Esc` behavior for popups, Vim insert mode, and
`/agent` editing while validating conflicts with fixed/backtrack and
request-input navigation bindings.
- Adds behavior and snapshot coverage for remapped interruption paths.

## How to Test

1. Run Codex and open `/keymap`, then set **Interrupt Turn** to `f12`.
2. Start a turn and confirm `Esc` no longer interrupts it while `f12`
does; the running hint should display `f12 to interrupt`.
3. Queue a steer while a turn is running and confirm the preview
displays `f12`; pressing it should interrupt and submit the steer
immediately.
4. Trigger a `request_user_input` prompt and confirm its footer uses
`f12`; with notes open, `Esc` should still clear notes while `f12`
interrupts the turn.
5. Clear the Interrupt Turn binding and confirm the key-specific
interrupt hint is removed while `Ctrl+C` remains available.

Targeted validation:

- `just write-config-schema`
- `just fix -p codex-config`
- `just fix -p codex-tui`
- `just fmt`
- `just argument-comment-lint-from-source -p codex-config -p codex-tui`
- `just test -p codex-config`
- `cargo insta pending-snapshots --manifest-path tui/Cargo.toml`
- `just test -p codex-tui keymap_setup::tests`
- `just test -p codex-tui` (fails in two pre-existing guardian
feature-flag tests unrelated to this diff; the intentional picker
snapshot updates were reviewed and accepted)

codex-rs/tui/src/chatwidget/interaction.rs

@@ -112,8 +112,7 @@ impl ChatWidget {
             return;
         }
 
-        if matches!(key_event.code, KeyCode::Esc)
-            && matches!(key_event.kind, KeyEventKind::Press | KeyEventKind::Repeat)
+        if self.chat_keymap.interrupt_turn.is_pressed(key_event)
             && !self.input_queue.pending_steers.is_empty()
             && self.bottom_pane.is_task_running()
             && self.bottom_pane.no_modal_or_popup_active()