[Docs] Preserve generated quantization URLs and link recipes in supported models

[hsliuustc0106]

Summary

• Route generated quantization pages under User Guide -> Features -> Quantization while preserving their existing user_guide/examples/quantization/<name>.md URLs.
• Do not add a Quantization section under Examples; if the Features -> Quantization target is unavailable, omit generated quantization examples from navigation and warn.
• Remove the existing examples/quantization/*.py example sources, so the current docs build emits no Quantization example links or pages.
• Add direct recipe links for the audited supported-model rows, preferring published recipes.vllm.ai pages and falling back to repository recipes.
• Update the hardware columns for those recipe-linked rows from explicit recipe evidence:
  • NVIDIA only: Qwen3-Omni, Qwen-Image, Qwen-Image-2512, Qwen3-TTS CustomVoice, and Higgs Audio V3 TTS.
  • NVIDIA and AMD: MiniMax H3.
• Keep recipe commands and validation details in the recipe files themselves; no separate coverage registry is introduced.

Source-of-truth boundaries

• The Recipe column in docs/models/supported_models.md is the direct mapping from a supported-model row to its deployment recipe.
• Published pages are preferred when available; otherwise the link points to the in-repository recipe.
• Only rows with an audited recipe link have recipe-derived hardware changes in this PR; unlinked rows retain their existing implementation-support metadata until their recipe is audited.
• Hardware marks are based on explicit recipe evidence. For Qwen3-Omni, the NVIDIA mark follows its explicit CUDA-based recipe commands; platform-delta configuration mentions alone are not treated as validation evidence.
• Recipe files under recipes/ remain the source of truth for commands and validation details.

Refs #5919

Validation

• Full CI-equivalent pre-commit suite — passed
• pytest -c /dev/null --confcutdir=tests/docs -q tests/docs/test_generate_examples.py — 5 passed
• No files remain under examples/quantization/
• git diff --check
• mkdocs build --strict passed on the pre-conflict-resolution commit
• Conflict resolved against latest main; final PR diff contains no TTS ratchet change

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[vllm-omni-review-bot]

模块负责人：@david6666666 @Isotr0py @lishunyang12

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