docs(ray): migrate guarded NPU quick start

[Meihan-chen]

Summary

• replace the generic Ray page with the executable two-NPU Quick Start validated in cosdt-ci-test/workflows
• preserve the existing cluster, Ray Job, environment-variable, and Dashboard guidance in a separate usage.rst page
• add the Ray documentation test and reusable-workflow caller
• update the Ray homepage card to distinguish general usage from the guarded Quick Start

Validation

• python -m unittest tests.ray.test_project_contract tests.ray.test_quick_start_ascend -v
• parsed the Markdown contract with 5 executable commands and 5 expected-output blocks
• actionlint .github/workflows/ray-quick-start.yml
• Sphinx HTML build succeeds; all emitted warnings are pre-existing in unrelated pages

This PR intentionally does not touch the upstream Ray examples guard. The new Quick Start retains the proven two-device discovery, Task/Actor allocation, ASCEND_RT_VISIBLE_DEVICES isolation, and real torch_npu worker operation.

[ascend-robot]

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[Meihan-chen]

/check-cla

[ascend-robot]

CLA Signature Pass

Meihan-chen, thanks for your pull request. All authors of the commits have signed the CLA. 👍

[github-actions]

📖 文档预览：https://ascend.github.io/docs/pr-preview/pr-161/sources/Ray/

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