Issue description

Since #3582, sigwinch is used to invalidate the OSC 11/10 cache. Since then, mode 2031 was created and it allows applications to listen for theme change events. tmux should listen to those events to invalidate it's own osc 11/10 cache.
It should also allow applications running inside tmux to listen to those events if requested.

You can find the specification for mode 2031 here: https://contour-terminal.org/vt-extensions/color-palette-update-notifications/

Required information

Please provide the following information:

• tmux version (tmux -V): tmux 3.5a
• Platform (uname -sp): Linux unknown
• $TERM inside and outside of tmux (echo $TERM): ghostty
• Logs from tmux (tmux kill-server; tmux -vv new): irrelevent