[XPU][CI/Release][3/N] Add xpu wheel release to release pipeline

[jikunshang]

Summary

This PR adds XPU wheel building and publishing support to the Buildkite release pipeline, enabling pre-built XPU wheels to be distributed via wheels.vllm.ai.

Changes

Release pipeline (release-pipeline.yaml)

• Add a new Build wheel - x86_64 - XPU step that builds the XPU wheel using Dockerfile.xpu and uploads it to S3.
• Rename the existing Publish XPU Triton shim index step to Publish and stage XPU Triton shim, and extend it to also stage the Triton shim wheel into the per-commit S3 directory so that the nightly index generator can pick it up.

Nightly index generation (generate-and-upload-nightly-index.sh, generate-nightly-index.py)

• Filter for vllm-* wheels when detecting the version from the commit directory, avoiding false matches on the Triton shim wheel.
• Recognize xpu as a known variant suffix in wheel filename parsing.
• Include triton-*+xpu-* wheels in release (non-nightly) index generation so the XPU Triton shim is co-published alongside the vLLM XPU wheel.

Triton shim publish script (publish-triton-shim.sh)

• Stage the Triton shim wheel into the per-commit S3 prefix (s3://vllm-wheels/$COMMIT/) so it is available alongside the vLLM XPU wheel.
• Add BUILDKITE_COMMIT validation and fix --wheel-dir / --output-dir paths.

Dockerfile.xpu (Dockerfile.xpu)

• Add a vllm-build multi-stage target that produces a standalone dist/*.whl artifact for CI wheel builds.
• Remove the manual triton/triton-xpu uninstall-reinstall workaround from the runtime stage (no longer needed with the Triton shim).

Documentation (gpu.xpu.inc.md)

• Replace "no pre-built XPU wheels" with installation instructions for nightly and per-commit wheels via wheels.vllm.ai.
• Document the triton==3.7.2+xpu shim and remove the manual triton-xpu swap instructions.

Test Plan

trigger release pipeline for this branch, https://buildkite.com/vllm/release-v2/builds/5120

Test Result

wheels can be found https://wheels.vllm.ai/9b7e36805bf42c0a23a58971fd72ba598fc1e984/xpu
or install by
uv pip install vllm --pre --extra-index-url=https://wheels.vllm.ai/9b7e36805bf42c0a23a58971fd72ba598fc1e984/xpu/ --extra-index-url=https://download.pytorch.org/whl/xpu --index-strategy unsafe-best-match

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Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.

[mergify]

Documentation preview: https://vllm--52108.org.readthedocs.build/en/52108/

[claude]

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[jikunshang]

/ci run

[github-actions]

✅ Triggered Buildkite CI #83845 for commit a7a79d0df5ee.