docs: update overall doc style

[adohe]

What does this PR do?

Update the overall documentation site style, to keep it more clean and technical.

Related issue

#106

Type of change

• 🐛 Bug fix
• ✨ New feature
• 💥 Breaking change (public API / CLI behavior changes in a non-backward-compatible way)
• 📝 Documentation update
• ♻️ Refactoring
• ⚡ Performance improvement
• ✅ Test coverage improvement

How was it tested?

Checklist

• The PR title summarizes the contribution.
• Linked the related issue in the description (if any).
• Existing tests pass (pytest tests/ -k cpu).
• New behavior is covered by tests.
• Described the test commands run and any hardware limitations.
• Public API / CLI changes are additive and backward-compatible (see CONTRIBUTING.md).

Breaking change details

[gemini-code-assist]

Code Review

This pull request updates the documentation layout and styling for AReno. It introduces a major CSS redesign, custom HTML layout components on the landing page, new templates for the header and sidebar, and updates to the Sphinx configuration. The reviewer feedback focuses on improving the readability of the .rst source by replacing HTML entity newlines with standard newlines in code blocks, adding double quotes to HTML attributes, wrapping hardcoded UI strings in translation functions for internationalization, and adding vendor prefixes and properties for better cross-browser CSS compatibility.

Important

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[xsuler]

/lgtm