docs: preserve legacy Leaderboard links and fragments

[ye1457]

Summary

Follow-up to merged #200, addressing the review about broken legacy links.

• Generate rst_source/benchmarks.html as a redirect to sibling leaderboard.html in both documentation builds.
• Use sphinx-reredirects==1.1.0, compatible with the existing Python 3.11 / Sphinx 8.1.3 documentation environment. Its default redirect preserves URL fragments using location.replace() and provides a no-JavaScript meta-refresh fallback.
• Keep the target relative so the language, documentation version and preview host remain unchanged.
• Keep Leaderboard as the only navigation entry and result page. No duplicate content, rendering implementation, dashboard-only configuration, or experiment changes.

This changes only docs/requirements.txt and the two conf.py files. All presentation assets continue to load from misc main.

Validation

• Full English and Chinese Sphinx builds with -E -a -W --keep-going: passed. Both outputs contain the generated legacy redirect page.
• 66 local browser/HTTP checks: passed. Covered both languages, latest/PR-like prefixes, plain and fragment URLs (including #libero-pro-astra-memory), actual destination scrolling, Back navigation without loops, no-JS destination readability, renderer failure, and directly opened local files.
• uv pip check: passed; only the new documentation extension was installed.
• Pre-commit and git diff --check: passed.
• Published Read the Docs previews: all 4 real-browser cases passed (English/Chinese, plain/fragment links). Old URLs return 200 and redirect to the same-language Leaderboard; the memory anchor is visible in the loaded interactive page.
• Remote CI passed: Python 3.10/3.11/3.12 unit tests, pre-commit, and both Read the Docs builds.
• No result data, denominators, robot code, planner code, media, or runtime dependencies changed.

The extension generates redirects into the HTML output, so the fix works on local builds and PR previews as well as the published site. It does not depend on Read the Docs project-dashboard redirects.

Preview

• English legacy URL with memory fragment
• Chinese legacy URL with memory fragment

[read-the-docs-community]

Documentation build overview

📚 RPent-cn | 🛠️ Build #34628939 | 📁 Comparing a0ad0ed against latest (886b3b2)

  🔍 Preview build  

1 file changed

+ rst_source/benchmarks.html

[read-the-docs-community]

Documentation build overview

📚 RPent | 🛠️ Build #34628937 | 📁 Comparing a0ad0ed against latest (886b3b2)

  🔍 Preview build  

1 file changed

+ rst_source/benchmarks.html