fix: Update torch to 2.3+ for transformers compatibility

transformers 4.44+ requires torch.utils._pytree.register_pytree_node
which was added in torch 2.3.0. Old torch 2.1.0 only had the
underscore-prefixed _register_pytree_node.

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

Co-Authored-By: Claude Opus 4.5 <[email protected]>

requirements.txt

@@ -6,7 +6,8 @@ python-multipart==0.0.6
 pydantic==2.5.0
 
 # Machine Learning
-torch==2.1.0
+# torch 2.3+ required for transformers 4.44+ (pytree API compatibility)
+torch>=2.3.0
 transformers>=4.44.0
 accelerate>=0.30.0