fix kitty detection in ssh wrapper function

Kitty doesn't set TERM_PROGRAM, check TERM=xterm-kitty instead.
Also use modern `kitten ssh` command.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

private_dot_config/private_fish/config.fish

@@ -55,8 +55,8 @@ if type -q ip
 end
 
 function s
-    if test "$TERM_PROGRAM" = kitty
-        kitty +kitten ssh $argv
+    if test "$TERM" = xterm-kitty
+        kitten ssh $argv
     else
         ssh $argv
     end