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/server-ui/scripts/comfyui/download-model.sh

@@ -0,0 +1,105 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+
+# shellcheck disable=SC1091
+source "${SCRIPT_DIR}/catalog-lib.sh"
+
+if [[ $# -lt 1 ]]; then
+  echo "Usage: $0 <catalog-model-id>"
+  echo ""
+  echo "Available models:"
+  catalog_list_ids | sed 's/^/  /'
+  exit 1
+fi
+
+MODEL_ID="$1"
+
+if ! catalog_list_ids | grep -qx "${MODEL_ID}"; then
+  echo "ERROR: Unknown model id: ${MODEL_ID}"
+  echo "Run: ${SCRIPT_DIR}/list-models.sh"
+  exit 1
+fi
+
+load_comfyui_stack_env
+
+DATA_ROOT="${DATA_ROOT:-/data}"
+catalog_ensure_dirs "${DATA_ROOT}"
+
+SOURCE="$(catalog_get_field "${MODEL_ID}" source)"
+NAME="$(catalog_get_field "${MODEL_ID}" name)"
+DEST="$(catalog_dest_path "${MODEL_ID}" "${DATA_ROOT}")"
+
+echo "=== Download: ${NAME} (${MODEL_ID}) ==="
+echo "Source: ${SOURCE}"
+echo "Target: ${DEST}"
+echo ""
+
+if [[ -f "${DEST}" ]]; then
+  echo "Already exists: ${DEST}"
+  echo ""
+  echo "Done."
+  exit 0
+fi
+
+mkdir -p "$(dirname "${DEST}")"
+
+# shellcheck disable=SC1091
+source "${SCRIPT_DIR}/download-http-lib.sh"
+
+case "${SOURCE}" in
+  huggingface)
+    HF_REPO="$(catalog_get_field "${MODEL_ID}" hf_repo)"
+    FILENAME="$(catalog_get_field "${MODEL_ID}" filename)"
+    DOWNLOAD_URL="$(catalog_get_field "${MODEL_ID}" download_url)"
+    HF_REVISION="$(catalog_get_field "${MODEL_ID}" hf_revision)"
+    REVISION="${HF_REVISION:-main}"
+
+    if [[ -n "${DOWNLOAD_URL}" ]]; then
+      URL="${DOWNLOAD_URL}"
+    elif [[ -n "${HF_REPO}" && -n "${FILENAME}" ]]; then
+      URL="https://huggingface.co/${HF_REPO}/resolve/${REVISION}/${FILENAME}"
+    else
+      echo "ERROR: Catalog entry missing download_url or hf_repo/filename"
+      exit 1
+    fi
+
+    download_http_file "${URL}" "${DEST}"
+    ;;
+  url)
+    DOWNLOAD_URL="$(catalog_get_field "${MODEL_ID}" download_url)"
+    if [[ -z "${DOWNLOAD_URL}" ]]; then
+      echo "ERROR: Catalog entry missing download_url"
+      exit 1
+    fi
+    download_http_file "${DOWNLOAD_URL}" "${DEST}"
+    ;;
+  civitai)
+    CIVITAI_MODEL_ID="$(catalog_get_field "${MODEL_ID}" civitai_model_id)"
+    if [[ -z "${CIVITAI_MODEL_ID}" ]]; then
+      echo "ERROR: Catalog entry missing civitai_model_id"
+      exit 1
+    fi
+    if [[ -z "${CIVITAI_TOKEN:-}" ]]; then
+      echo "ERROR: CIVITAI_TOKEN not set in stacks/comfyui/.env"
+      exit 1
+    fi
+    curl -fL \
+      -H "Authorization: Bearer ${CIVITAI_TOKEN}" \
+      -o "${DEST}" \
+      "https://civitai.com/api/download/models/${CIVITAI_MODEL_ID}"
+    ;;
+  *)
+    echo "ERROR: Unknown source: ${SOURCE}"
+    exit 1
+    ;;
+esac
+
+if [[ ! -f "${DEST}" ]]; then
+  echo "ERROR: Download finished but file missing: ${DEST}"
+  exit 1
+fi
+
+echo ""
+echo "Done."