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/verify-api-key.sh

@@ -0,0 +1,42 @@
+#!/usr/bin/env bash
+# Verify API_KEY from /opt/control-plane/.env against live server-ui.
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+# shellcheck source=print-api-key-instructions.sh
+source "${SCRIPT_DIR}/print-api-key-instructions.sh"
+
+PROD_ENV="/opt/control-plane/.env"
+UI_PORT=8091
+
+if [[ -f "${PROD_ENV}" ]]; then
+  UI_PORT="$(grep '^SERVER_UI_PORT=' "${PROD_ENV}" 2>/dev/null | cut -d= -f2- || true)"
+  if [[ -z "${UI_PORT}" ]]; then
+    UI_PORT="$(sudo grep '^SERVER_UI_PORT=' "${PROD_ENV}" 2>/dev/null | cut -d= -f2- || true)"
+  fi
+fi
+[[ -n "${UI_PORT}" ]] || UI_PORT=8091
+
+api_key="$(_read_api_key "${PROD_ENV}")"
+
+if [[ -z "${api_key}" && -r "${SCRIPT_DIR}/../../control-plane/.env" ]]; then
+  api_key="$(_read_api_key "${SCRIPT_DIR}/../../control-plane/.env")"
+fi
+
+if [[ -z "${api_key}" ]]; then
+  echo "FAIL: brak API_KEY w ${PROD_ENV}"
+  exit 1
+fi
+
+if curl -sf -X POST "http://127.0.0.1:${UI_PORT}/api/auth/verify" \
+  -H "Content-Type: application/json" \
+  -d "{\"api_key\":\"${api_key}\"}" >/dev/null; then
+  echo "OK: klucz z ${PROD_ENV} działa na http://127.0.0.1:${UI_PORT}"
+  exit 0
+fi
+
+echo "FAIL: klucz z ${PROD_ENV} odrzucony przez server-ui (:${UI_PORT})"
+echo "  Uruchom: bash ${SCRIPT_DIR}/show-api-key.sh"
+echo "  Sync env: sudo bash ${SCRIPT_DIR}/setup-control-plane-env.sh"
+echo "  Restart:  sudo systemctl restart server-ui"
+exit 1