feat: add macOS support to uv lockfile and torch sources (#61)

The lockfile was restricted to `sys_platform == 'linux'`, so `uv run
pixelshot` failed on macOS.  Add darwin to the environments list, gate
the CUDA torch index and nvidia-cudnn override behind a Linux marker so
macOS resolves CPU-only wheels from PyPI instead.

Author: yichuan-w

pyproject.toml

@@ -96,12 +96,12 @@ include = [
 ]
 
 [tool.uv]
-override-dependencies = ["nvidia-cudnn-cu12==9.20.0.48"]
-environments = ["sys_platform == 'linux'"]
+override-dependencies = ["nvidia-cudnn-cu12==9.20.0.48; sys_platform == 'linux'"]
+environments = ["sys_platform == 'linux'", "sys_platform == 'darwin'"]
 
 [tool.uv.sources]
-torch = [{ index = "pytorch-cu129" }]
-torchvision = [{ index = "pytorch-cu129" }]
+torch = [{ index = "pytorch-cu129", marker = "sys_platform == 'linux'" }]
+torchvision = [{ index = "pytorch-cu129", marker = "sys_platform == 'linux'" }]
 
 [[tool.uv.index]]
 name = "pytorch-cu129"