[Feature Request] Add customizable interrupt prompt text in settings.json

Bug Description
Title: Allow customizing the interrupt prompt text ("Interrupted · What should Claude do instead?")

Request:

Claude Code already exposes user-facing UI text customization via spinnerVerbs / spinnerWords / spinnerTips in settings.json. Please extend that same pattern to the interrupt line shown when I press Esc:

⎿ Interrupted · What should Claude do instead?

Right now this string is hardcoded and can't be overridden through settings, env vars, or themes.

Proposed shape — mirror the existing spinner config so it's consistent:

{ …
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