Feat: No Quit/Cancel Button in Debate Setup

### Feature

### There is currently no **Quit/Cancel** button available in the **Debate Setup** modal.

If a user enters the debate setup but decides not to participate, there is no clear option to exit or cancel the debate. The only available action is **"I'm Ready"**, which proceeds with the debate setup.

## Expected Behavior

A **Quit**, **Cancel**, or **Leave Debate** button should be provided so that users can exit the debate setup without starting the debate.

## Suggested Solution

Add a secondary button such as:
- **Leave Debate**

The button could be placed next to the **"I'm Ready"** button or in the top-right corner of the modal.

## Screenshot

The current Debate Setup modal does not provide any option to cancel or quit the debate.

### Additional Context

### Code of Conduct

- [x] I have joined the [Discord server](https://discord.gg/hjUhu33uAn) and will post updates there
- [x] I have searched existing issues to avoid duplicates

Locate the Debate Setup modal and its “I'm Ready” action in the TypeScript frontend. Add a visible cancel or leave action that exits without starting the debate, then run the relevant frontend checks and confirm both actions behave correctly.

Written by the indexing model from the issue text.