Support full-width chat layout on larger screens

### Feature summary

_No response_

### What problem are you trying to solve?

The chat interface currently has a fixed maximum width, even on large displays. This can make it difficult to read wide content such as code diffs and formatted output during a conversation.

### Proposed solution

A setting or toggle to enable a full-width chat layout would improve readability and make better use of available screen space, particularly for developer workflows and large monitors.

Potential solutions:
- A user preference for “Full Width Chat”

### Workflow impact

_No response_

### Installation context

_No response_

### Additional context