feat: Implement MetaHub Save Image node for ComfyUI

Complete implementation of advanced image saving node with dual metadata:
- A1111/Civitai compatible metadata (tEXt chunk "parameters")
- Image MetaHub metadata (iTXt chunk "imagemetahub_data")
- Auto-detection of LoRAs from workflow (UI and API formats)
- SHA256 hash calculation (AutoV2/Civitai format) with caching
- Graceful degradation (never interrupts generation)
- IMH Pro fields support (user_tags, notes, project_name)
- Auto-increment filenames with customizable output paths

Files added:
- metahub_save_node.py: Main node class with INPUT_TYPES
- metadata_utils.py: Hash calculation, metadata formatting, PNG injection
- __init__.py: Node registration for ComfyUI
- requirements.txt: Dependencies (Pillow, numpy)
- README.md: Installation and usage documentation

100% compatible with Image MetaHub comfyUIParser.ts specification.

__init__.py

@@ -0,0 +1,16 @@
+"""
+MetaHub Save Image - ComfyUI Custom Node
+Entry point for node registration
+"""
+
+from .metahub_save_node import MetaHubSaveNode
+
+NODE_CLASS_MAPPINGS = {
+    "MetaHubSaveNode": MetaHubSaveNode
+}
+
+NODE_DISPLAY_NAME_MAPPINGS = {
+    "MetaHubSaveNode": "MetaHub Save Image"
+}
+
+__all__ = ["NODE_CLASS_MAPPINGS", "NODE_DISPLAY_NAME_MAPPINGS"]