fish: auto attach or create tmux session named "default"

dot_config/private_fish/config.fish.tmpl

@@ -12,6 +12,10 @@ if status --is-interactive
     set -q fish_private_mode && set -x FISH_IS_IN_PRIVATE 1
     command -v zoxide > /dev/null && zoxide init fish | source
     command -v starship > /dev/null && starship init fish | source
+
+    if type -q tmux; and test -z "$TMUX"
+        tmux attach -t default || tmux new-session -s default
+    end
 end
 
 {{- if (and (eq .chezmoi.os "linux") (eq .hosttype "desktop" "laptop")) }}