Increase chat section width, and size of text area for large prompts

The prompt input textarea should make better use of available screen estate for large inputs. Height could increase up to nearly full viewport height for large inputs. Good prompts are often very long, this helps writing and checking the prompt. Prompt input box could also be wider, see next point.

For reading conversations the width should also be increased (depending on available space). Maybe it could be user configurable (e.g. narrow, medium, wide). One use case is responses with long code blocks with long lines: then we need to scroll right which should be unnecessary when you have available space, and also the scroll bar at the bottom of the code block might not be visible for long code blocks.