[feat] add Liger-Kernel doc

[zheliuyu]

Summary

Add Ascend NPU documentation for Liger-Kernel and integrate it into the Ascend open-source documentation portal.

• Add a new sources/liger-kernel/ section with installation and quick start guides
• Add a Liger-Kernel project card under Operator Development & Programming on the homepage
• Register the docs entry in the sidebar toctree
• Add the Liger-Kernel logo (_static/images/Liger-Kernel.png)
• Fix the quick start demo script to use apply_liger_kernel_to_qwen3 and include a model patch verification step

Changes

Installation Guide (install.rst)

• Document Liger-Kernel v0.8.0+ support for Ascend NPU
• Provide source installation steps (pip install -e ".[dev]")
• Include a LigerRMSNorm environment verification script

Quick Start (quick_start.rst)

• Add a model Patch API example for Qwen3
• Add a standalone operator example (LigerRMSNorm + LigerFusedLinearCrossEntropyLoss)
• Document integration with training frameworks such as LLaMA-Factory, VeOmni, and verl

[ascend-robot]

CLA Signature Pass

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

[zheliuyu]

The test results are as follows:

[zheliuyu]

/LGTM