Add swipe-down aux screen (SOCKTOP_AUX_CMD)

A separate tmux window running any TUI, reached with a vertical swipe from
any carousel screen; swiping up returns to the exact window/zoom you left.
The aux window is excluded from the horizontal carousel and horizontal
swipes on it are inert. Bound only when SOCKTOP_AUX_CMD is set.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

socktop-rack

@@ -13,6 +13,7 @@ done
 : "${SOCKTOP_HOSTS:=}"
 : "${SOCKTOP_SESSION:=socktop4}"
 : "${SOCKTOP_BIN:=socktop}"
+: "${SOCKTOP_AUX_CMD:=}"
 
 # Legacy form: SOCKTOP_HOSTS alone is a single tiled group.
 if [ -z "$SOCKTOP_GROUPS" ]; then
@@ -68,6 +69,11 @@ for group in $SOCKTOP_GROUPS; do
 done
 IFS=$old_ifs
 
+# The aux window sits outside the carousel; socktop-swipe recognises it by name.
+if [ -n "$SOCKTOP_AUX_CMD" ]; then
+	tmux new-window -d -t "$SOCKTOP_SESSION" -n aux "$SOCKTOP_AUX_CMD"
+fi
+
 tmux select-window -t "$SOCKTOP_SESSION:g0"
 
 tmux set-option -t "$SOCKTOP_SESSION" pane-border-status top