refactor: update artifact_huggingface_download.sh to use dest paths without type field

Updated link_model() and verify_model_links() functions to:
- Extract target directory directly from dest path (e.g., "checkpoints/model.safetensors")
- Remove model_type parameter from function signatures
- Support multiple target directories per model when files go to different locations
- Simplified function calls throughout the script

Also added bin/ directory to .gitignore allowlist to track utility scripts.

This change complements the models_huggingface.yaml refactoring that embedded
the type directory in the dest paths.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

.gitignore

@@ -20,6 +20,8 @@
 !.hushlogin
 !arty.yml
 !signature.txt
+!bin/
+!bin/**
 
 # Ignore so we won't commit these in the allowed dirctories.
 .DS_Store