Add auto-detection for Intel GPUs (#14386)

## Summary

This PR intends to enable `--torch-backend=auto` to detect Intel GPUs
automatically:
- On Linux, detection is performed using the `lspci` command via
`Display controller` id.
- On Windows, ~~detection is done via a `powershell` query to
`Win32_VideoController`~~. Skip support for now—revisit once a better
solution is available.

Currently, Intel GPUs (XPU) do not rely on specific driver or toolkit
versions to distribute different PyTorch wheels.

## Test Plan

<!-- How was it tested? -->
On Linux:

![image](https://github.com/user-attachments/assets/f7f238e3-a797-42ea-b8fa-9b028dfd4db5)
~~On Windows:

![image](https://github.com/user-attachments/assets/a10d774e-1cb9-431b-bb85-e3e8225df98f)~~

---------

Co-authored-by: Charlie Marsh <charlie.r.marsh@gmail.com>

docs/guides/integration/pytorch.md

@@ -444,10 +444,10 @@ $ # With an environment variable.
 $ UV_TORCH_BACKEND=auto uv pip install torch
 ```
 
-When enabled, uv will query for the installed CUDA driver and AMD GPU versions then use the
-most-compatible PyTorch index for all relevant packages (e.g., `torch`, `torchvision`, etc.). If no
-such GPU is found, uv will fall back to the CPU-only index. uv will continue to respect existing
-index configuration for any packages outside the PyTorch ecosystem.
+When enabled, uv will query for the installed CUDA driver, AMD GPU versions, and Intel GPU presence,
+then use the most-compatible PyTorch index for all relevant packages (e.g., `torch`, `torchvision`,
+etc.). If no such GPU is found, uv will fall back to the CPU-only index. uv will continue to respect
+existing index configuration for any packages outside the PyTorch ecosystem.
 
 You can also select a specific backend (e.g., CUDA 12.6) with `--torch-backend=cu126` (or
 `UV_TORCH_BACKEND=cu126`):
@@ -460,4 +460,12 @@ $ # With an environment variable.
 $ UV_TORCH_BACKEND=cu126 uv pip install torch torchvision
 ```
 
+On Windows, Intel GPU (XPU) is not automatically selected with `--torch-backend=auto`, but you can
+manually specify it using `--torch-backend=xpu`:
+
+```shell
+$ # Manual selection for Intel GPU.
+$ uv pip install torch torchvision --torch-backend=xpu
+```
+
 At present, `--torch-backend` is only available in the `uv pip` interface.