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/comfyui_config.py

@@ -0,0 +1,53 @@
+"""Shared ComfyUI paths and constants for Server UI integration."""
+
+from __future__ import annotations
+
+from pathlib import Path
+
+COMFYUI_CONTAINER = "comfyui"
+CONTAINER_MODELS_ROOT = "/root/ComfyUI/models"
+CONTAINER_WORKFLOWS_ROOT = "/root/ComfyUI/user/default/workflows"
+HOST_DATA_SUBDIR = "apps/comfyui"
+STACK_ID = "comfyui"
+CATALOG_FILENAME = "comfyui-models.catalog.yaml"
+
+
+def server_ui_root(base: Path | None = None) -> Path:
+    return base or Path(__file__).resolve().parent
+
+
+def catalog_path(base: Path | None = None) -> Path:
+    return server_ui_root(base) / CATALOG_FILENAME
+
+
+def scripts_dir(base: Path | None = None) -> Path:
+    return server_ui_root(base) / "scripts" / "comfyui"
+
+
+def stack_env_path(repo_root: Path) -> Path:
+    return repo_root / "stacks" / "comfyui" / ".env"
+
+
+def host_models_root(data_root: Path) -> Path:
+    return data_root / HOST_DATA_SUBDIR / "models"
+
+
+def host_workflows_dir(data_root: Path) -> Path:
+    return data_root / HOST_DATA_SUBDIR / "workflows"
+
+
+def host_custom_nodes_dir(data_root: Path) -> Path:
+    return data_root / HOST_DATA_SUBDIR / "custom_nodes"
+
+
+def container_model_path(relative: str) -> str:
+    return f"{CONTAINER_MODELS_ROOT}/{relative.lstrip('/')}"
+
+
+def container_workflow_path(relative: str) -> str:
+    return f"{CONTAINER_WORKFLOWS_ROOT}/{relative.lstrip('/')}"
+
+
+def host_to_container_model_path(host_path: Path, data_root: Path) -> str:
+    rel = host_path.resolve().relative_to(host_models_root(data_root).resolve())
+    return container_model_path(rel.as_posix())