docker-stacks-update: fix --list freeze + unbound variable

- Add missing 'shift' in --list case (caused infinite loop)
- Initialize color vars to empty strings before tput block
  (set -u errored when tput unavailable or non-TTY)

docker-stacks-update/docker-stacks-update.sh

@@ -10,6 +10,7 @@
 set -euo pipefail
 
 # ── Terminal colours ──────────────────────────────────────────────
+BOLD=""; RED=""; GREEN=""; YELLOW=""; CYAN=""; RESET=""
 if command -v tput >/dev/null 2>&1 && [ -t 1 ]; then
   BOLD=$(tput bold 2>/dev/null || true)
   RED=$(tput setaf 1 2>/dev/null || true)
@@ -21,6 +22,7 @@ fi
 
 # ── State ───────────────────────────────────────────────────────────
 TARGET_STACKS=()     # user-specified stacks (empty = all)
+LIST_ONLY=false      # --list flag
 all_names=()         # pre-filter stack names (for error messages)
 updated_names=()     # stack names that were updated
 updated_detail=()    # parallel: "stack: service1, service2"
@@ -45,6 +47,7 @@ that have updates.
 
 Options:
   -h, --help              Show this help message
+  -l, --list              List running stacks and exit
   -s, --stack <name>      Target a specific stack (repeatable)
 
 No options = update all running stacks.
@@ -56,6 +59,7 @@ EOF
 while [[ $# -gt 0 ]]; do
   case "$1" in
     -h|--help) usage ;;
+    -l|--list) LIST_ONLY=true; shift ;;
     -s|--stack)
       shift
       [[ $# -eq 0 ]] && { echo -e " ${RED}✗${RESET} Option --stack requires a name." >&2; exit 1; }
@@ -103,6 +107,10 @@ for name in "${names[@]}"; do
 done
 echo ""
 
+if $LIST_ONLY; then
+  exit 0
+fi
+
 # ── Spinner for long operations ─────────────────────────────────────
 _spin_kill=""