refactor nodes into standalone file

backend/nodes/folder.py

@@ -0,0 +1,29 @@
+from __future__ import annotations
+from backend.node_registry import register_node
+from backend.nodes.helpers import list_folder_paths
+
+
+@register_node(display_name="Folder")
+class Folder:
+    @classmethod
+    def INPUT_TYPES(cls):
+        return {
+            "required": {
+                "folder": ("FOLDER_PICKER", {"default": "", "placement": "top"}),
+            }
+        }
+
+    RETURN_TYPES = ("DIRECTORY",)
+    RETURN_NAMES = ("directory",)
+    FUNCTION = "list_files"
+
+    DESCRIPTION = (
+        "Pick a folder and output its directory path plus one file socket per compatible image, array, or SPM file inside it. "
+        "Supported files include common images, .npy/.npz arrays, and .gwy/.sxm/.ibw scans."
+    )
+
+    def list_files(self, folder: str) -> tuple:
+        entries = list_folder_paths(folder)
+        if not entries:
+            return tuple()
+        return tuple(item["path"] for item in entries)