hosts: homes: mousqueton: fix `tmux` 24-bit color

This is based on this answer [1] from Stack Overflow.

I'll have to look into what the proper fix would be in general, this is
just a band-aid to get it working correctly while SSH-ing from my
laptop.

[1]: https://stackoverflow.com/a/41786092

hosts/homes/ambroisie@mousqueton/default.nix

@@ -19,4 +19,9 @@
 
   # I use scripts that use the passthrough sequence often on this host
   my.home.tmux.enablePassthrough = true;
+
+  programs.tmux.extraConfig = ''
+    # Setup 24-bit color explicitly, as the default terminfo entry does not
+    set-option -sa terminal-overrides ",xterm-256color:Tc"
+  '';
 }