Fix uv index: Use explicit=true for PyTorch index

- Added explicit=true to pytorch-cu121 index
- Only torch, torchvision, torchaudio use PyTorch index
- All other packages (requests, fastapi, etc.) use PyPI
- Fixes: requests version conflict (PyTorch index has 2.28.1, we need >=2.31.0)

How explicit=true works:
- PyTorch index only checked for packages listed in tool.uv.sources
- Prevents dependency confusion and version conflicts
- Best practice for supplemental package indexes

pyproject.toml

@@ -59,13 +59,18 @@ dev = [
 
 # Add PyTorch CUDA index as additional source
 # CUDA builds work on both GPU and CPU systems (fallback to CPU if no GPU)
+# Using 'explicit = true' means only packages we explicitly specify use this index
 [[tool.uv.index]]
 name = "pytorch-cu121"
 url = "https://download.pytorch.org/whl/cu121"
+explicit = true
 
-# Tell uv to get torch from the PyTorch CUDA index
+# Tell uv to get torch, torchvision, and torchaudio from the PyTorch CUDA index
+# All other packages come from PyPI
 [tool.uv.sources]
 torch = { index = "pytorch-cu121" }
+torchvision = { index = "pytorch-cu121" }
+torchaudio = { index = "pytorch-cu121" }
 
 [tool.ruff]
 line-length = 100