Add Qwen3-Next tutorials

[ming1212]

What this PR does / why we need it?

Does this PR introduce any user-facing change?

How was this patch tested?

• vLLM version: v0.11.2
• vLLM main: https://github.com/vllm-project/vllm/commit/v0.11.2

[gemini-code-assist]

Code Review

This pull request significantly enhances the documentation by adding a comprehensive tutorial for the Qwen3-Next model. The previous document has been renamed and expanded to include a detailed introduction, setup instructions, inference examples, and guidelines for accuracy and performance evaluation. The updated index.md correctly reflects the new tutorial file. These changes will be very helpful for users looking to get started with Qwen3-Next on vLLM Ascend. The new tutorial is well-structured and provides clear, step-by-step instructions.

[github-actions]

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