Add search weighting and ranking documentation

[devin-ai-integration]

Summary

Adds a new "How results are ranked" section to the existing Search configuration page, documenting how Fern's Algolia DocSearch weighs and ranks search attributes. This was requested by a customer who wanted transparency into search behavior.

The new section uses an AccordionGroup with four expandable panels:

• Attribute weighting — priority-ordered table of all 11 searchable attributes. Keywords are ranked feat(ci): Add stale-bot #1 (above page title).
• Tiebreaking — custom ranking rules (date, version index, page position) and deduplication behavior
• Page hierarchy — clarifies that navigation hierarchy doesn't affect ranking, but heading depth within a page does
• Empty result handling — explains the allOptional fallback and which terms are treated as optional

Also updates the page's meta description. The attribute weighting and ranking details were derived from the actual Algolia configuration in fern-platform (set-index-settings.ts and types.ts).

Updates since last revision

• Moved Keywords to priority feat(ci): Add stale-bot #1 in the attribute weighting table (above Page title), per reviewer request.
• Resolved merge conflict with upstream changes that restructured the content into an AccordionGroup layout.

Review & Testing Checklist for Human

• Verify keywords-first ranking is intentional — the docs now show Keywords as priority feat(ci): Add stale-bot #1, but the actual SEARCHABLE_ATTRIBUTES in types.ts lists title first. Confirm whether the Algolia config is being updated to match, or if the docs should reflect the current config order.
• Check that internal links resolve — especially /learn/docs/configuration/page-level-settings#document-properties, /learn/docs/configuration/page-level-settings#title, /learn/docs/writing-content/markdown-basics#page-header, and /learn/docs/writing-content/components/code-blocks.
• Preview the rendered page — verify the accordion components render correctly and the markdown table inside the "Attribute weighting" accordion displays properly.

Suggested test plan: Open the preview link, expand each accordion, click each internal link, and confirm the table renders with correct priority ordering.

Notes

• This documents current implementation behavior. If the Algolia config in fern-platform changes, this page will need a corresponding update.
• A changelog entry (2026-03-27.mdx) was added in an earlier commit.

Link to Devin session: https://app.devin.ai/sessions/c8f263074a264d729af53cbab8b8b5b0
Requested by: @devalog

[devin-ai-integration]

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[github-actions]

🌿 Preview your docs: https://fern-preview-devin-1774630820-search-weighting-docs.docs.buildwithfern.com/learn

Here are the markdown pages you've updated:

• learn/docs/customization/search