[codex] Add sheet keybinding selector

[cormoran]

Summary

• Change the key binding selector from a centered modal to a bottom sheet on tablet and wider screens.
• Keep the mobile selector full-screen while making wide layouts leave the keymap preview visible above the sheet.
• Scroll the keymap page so the selected key is centered in the remaining visible preview area.

Validation

• npm run format:check
• npm run lint
• npm test -- --runInBand
• npm run build

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[github-actions]

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_{Deployed from commit 906e561}