Fix .gitignore and add missing refnet/models/__init__.py

- Changed 'models' to '/models' so only root models/ dir is ignored,
not refnet/models/ subdirectory
- Add empty __init__.py to make refnet.models importable as a package

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

.gitignore

@@ -1,6 +1,6 @@
 .idea
 .vscode
-models
+/models
 *safetensors
 __pycache__
 preprocessor/weights