Bug Report: Improved Shell Window Resizing Support

Currently, resizing the Multipass shell window does not always result in a smooth adjustment of the shell content or layout. It would be helpful to automatically adapt the shell buffer and terminal layout to fit the new window size dynamically, just like modern terminal emulators do.

This would include:

- Reflowing or adjusting the shell content as the window is resized

- Avoiding layout glitches or scrollback issues when changing dimensions

- Provides a smoother, more responsive user experience

- Aligns Multipass with behavior users expect from modern terminal environments

- Especially useful when working with complex output or split-screen workflows

Start by reproducing the Multipass shell behavior while resizing its window, focusing on content reflow, terminal layout changes, and scrollback glitches. Trace the shell's terminal resizing path and define done as smooth adaptation to the new dimensions without layout or scrollback issues.

Written by the indexing model from the issue text.