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/control-plane/env_loader.py

@@ -87,6 +87,44 @@ def control_plane_env_paths(stack_dir: Path) -> list[Path]:
     return paths
 
 
+def _has_stack_compose(repo_root: Path) -> bool:
+    stacks = repo_root / "stacks"
+    if not stacks.is_dir():
+        return False
+    for name in ("compose.yaml", "docker-compose.yml", "docker-compose.yaml"):
+        if (stacks / "localai" / name).is_file():
+            return True
+    return False
+
+
+def _production_repo_root_candidates() -> list[Path]:
+    home = Path.home()
+    return [
+        home / "cursor" / "ubuntu-bare-metal",
+        Path("/data/apps/ubuntu-bare-metal"),
+        Path("/repo"),
+        home / "ubuntu-bare-metal",
+    ]
+
+
+def resolve_repo_root(stack_dir: Path, env: dict[str, str]) -> Path:
+    """Resolve ubuntu-bare-metal repo root for compose stack paths."""
+    for key in ("REPO_ROOT",):
+        raw = (env.get(key) or os.environ.get(key) or "").strip()
+        if raw:
+            candidate = Path(raw).expanduser().resolve()
+            if _has_stack_compose(candidate):
+                return candidate
+
+    if _is_production_stack_dir(stack_dir):
+        for candidate in _production_repo_root_candidates():
+            resolved = candidate.expanduser().resolve()
+            if _has_stack_compose(resolved):
+                return resolved
+
+    return (stack_dir.parent.parent).resolve()
+
+
 def api_key_source(stack_dir: Path, values: dict[str, str]) -> str:
     """Human-readable hint for logs (no secret values)."""
     if os.environ.get("API_KEY"):