Initial commit: VACE Mask Generator custom node

Single ComfyUI node implementing 5 VACE mask generation modes
(End/Pre/Middle/Edge/Join Extend) with zero external dependencies.
Replaces ~149 nodes from the original logic.json workflow.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

__init__.py

@@ -0,0 +1,3 @@
+from .nodes import NODE_CLASS_MAPPINGS, NODE_DISPLAY_NAME_MAPPINGS
+
+__all__ = ["NODE_CLASS_MAPPINGS", "NODE_DISPLAY_NAME_MAPPINGS"]