style(shell): improve shell script formatting and quoting

Apply shfmt formatting and fix some schellcheck complaints.

libexec/tmuxifier-commands

@@ -16,7 +16,8 @@ fi
 
 shopt -s nullglob
 
-{ for path in ${PATH//:/$'\n'}; do
+{
+  for path in ${PATH//:/$'\n'}; do
     for command in "${path}/tmuxifier-"*; do
       command="${command##*tmuxifier-}"
       echo "$command"