Add stack Update, ComfyUI model manager, and slim ComfyUI stack.

Server UI gains Update on stack cards, ComfyUI Models tab with workflow
scan and downloads, and centralized comfyui_config. Model catalog and
download scripts move from stacks/comfyui to server-ui so ComfyUI stays a
minimal Docker wrapper for easier image updates.

stacks/vllm/scripts/pull.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+STACK_DIR="$(cd "${SCRIPT_DIR}/.." && pwd)"
+
+cd "${STACK_DIR}"
+
+if [[ -f .env ]]; then
+  set -a
+  # shellcheck disable=SC1091
+  source .env
+  set +a
+fi
+
+if ! docker info &>/dev/null; then
+  echo "ERROR: Docker is not running"
+  exit 1
+fi
+
+echo "=== vLLM — pull image only (no start) ==="
+docker compose --profile vllm pull
+
+echo ""
+echo "Done. Start with: ./scripts/start.sh"