Never change the window's width

[jpmelos]

Keep the width of the Augment chat window always the same. This will prevent the window from changing size when you delete another window, for example, and Vim rebalances the remaining windows.

[mgmonteleone]

^{Code Review Agent🛡️ with @mgmonteleone's authorization}

Verdict: APPROVE

This is a focused improvement to the chat panel window setup. Setting winfixwidth on the chat window makes sense: the chat panel is a dedicated side panel, and keeping its width stable avoids surprising resizes when other windows are closed or Vim rebalances layout.

Non-blocking suggestion

Consider adding an opt-out guard, for example a global such as g:augment_disable_chat_fixed_width, before setting winfixwidth. Some users have highly customized window-management workflows and may prefer the panel to participate in normal width rebalancing. That does not need to block this PR, but it would make the behavior easier to override if needed.

[mgmonteleone]

This is a great addition for panel stability. I've implemented a g:augment_disable_chat_fixed_width opt-out in a separate branch (feature/au-21917-vim-pr-audit) to satisfy users who prefer dynamic resizing. I suggest incorporating that guard. Otherwise, LGTM.