Ctrl-c has too many overloads, which makes it do unexpected actions

### Describe the feature or problem you'd like to solve

Ctrl-c has too many overloads

### Proposed solution

I'm not sure what would be best here, but Ctrl-c should have only one clear action, not many overloads like "copy", "empty current prompt line" and "cancel current action".

### Example prompts or workflows

Once when I tried to copy some text from a question asked by copilot, it cancelled the question, so I was unable to answer it.

### Additional context

_No response_

Start by reproducing the reported Ctrl-C behavior in the Copilot CLI, including copying text from a question and cancelling or clearing an active prompt. Read the CLI's input-handling entry point and document the intended single action before changing anything. Done means the chosen Ctrl-C behavior is consistent across these workflows and the regression cases are covered.

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