Fix torch/transformers version incompatibility

Fix for: AttributeError: module 'torch.utils._pytree' has no attribute 'register_pytree_node'

Root Cause:
- torch==2.1.0 is too old for transformers>=4.46.0
- transformers 4.46+ uses register_pytree_node API
- This API only exists in torch 2.2+

Solution:
- Upgrade to torch>=2.2.0,<2.6.0
- Ensures compatibility with transformers 4.46+
- Still uses CPU-only torch from PyPI
- Cap at <2.6.0 for stability

Version Matrix:
✅ torch 2.2.0+ : transformers 4.46+ : Compatible
❌ torch 2.1.0 : transformers 4.46+ : Incompatible (pytree API missing)

This allows transformers to properly initialize with torch 2.2+.

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

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

requirements.txt

@@ -22,7 +22,7 @@ aiosqlite>=0.19.0
 numpy>=1.24.3,<2.0.0
 
 # HuggingFace dependencies (for Granite 4 local loading)
-# Install torch CPU version from PyPI (smaller, faster build)
-torch==2.1.0
+# Torch 2.2+ required for transformers 4.46+
+torch>=2.2.0,<2.6.0
 transformers>=4.46.0
 accelerate>=0.20.0  # For efficient model loading