refactor nodes into standalone file

backend/nodes/font_node.py

@@ -0,0 +1,36 @@
+from __future__ import annotations
+from backend.node_registry import register_node
+from backend.data_types import CUSTOM_FILE_FONT, SYSTEM_DEFAULT_FONT, list_overlay_font_choices, normalize_font_spec
+
+
+@register_node(display_name="Font")
+class Font:
+    @classmethod
+    def INPUT_TYPES(cls):
+        return {
+            "required": {
+                "family": ([SYSTEM_DEFAULT_FONT, *list_overlay_font_choices(), CUSTOM_FILE_FONT], {
+                    "default": SYSTEM_DEFAULT_FONT,
+                }),
+                "font_file": ("FILE_PICKER", {
+                    "default": "",
+                    "show_when_widget_value": {"family": [CUSTOM_FILE_FONT]},
+                }),
+            }
+        }
+
+    RETURN_TYPES = ("FONT",)
+    RETURN_NAMES = ("font",)
+    FUNCTION = "build"
+
+    DESCRIPTION = (
+        "Build a reusable font spec for annotation overlays. Choose a discovered system font, "
+        "use the default fallback stack, or point to a custom font file."
+    )
+
+    def build(self, family: str, font_file: str = "") -> tuple:
+        if family == SYSTEM_DEFAULT_FONT:
+            return (None,)
+        if family == CUSTOM_FILE_FONT:
+            return (normalize_font_spec({"path": font_file}),)
+        return (normalize_font_spec({"family": family}),)