[docs][serve] Fix Serve LLM examples sidebar doc links 404

[ryankert01]

Why?

When clicked on the sidebar of ray serve -> Serving llms -> examples -> serve small llms(or any others in this dir), they 404ed.

Summary

Fix stale Serve LLM tutorial links after deployment-serve-llm moved to sphinx_collections output under /_collections. Clicking the Serve LLM entries from the sidebar could still open the old path and 404.

• Canonicalize legacy sidebar/docs URLs to the fetched _collections pages.
• Add lightweight redirects for old serve/tutorials/deployment-serve-llm/... paths.
• Harden the rewrite for release-version docs URLs and safe JS redirect escaping.

Root Cause

The tutorials should be preserved. The in-tree copies were removed after the collection move, but some generated/sidebar links still used the old path shape.

Validation

• python -m compileall -q doc/source/conf.py doc/source/custom_directives.py
• git diff --check -- doc/source/conf.py doc/source/custom_directives.py
• Focused Python checks for URL rewrites, redirects, and double-content legacy paths.
• Pre-commit path checked; repo hooks skip doc/source/ by config.

[gemini-code-assist]

Code Review

This pull request introduces mechanism to rewrite legacy deployment serve LLM links and generate HTML redirects for legacy templates. The feedback highlights three key improvement opportunities: making the URL matching regex more robust by using a wildcard instead of hardcoded version segments, fixing a potential redirect bug caused by HTML-escaping inside a JavaScript block (suggesting json.dumps instead), and handling double content segments in legacy paths within canonicalize_collection_href to prevent broken links.

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[kouroshHakha]

@dstrodtman can you review this ?