DX-049: Build a useful docs 404 page

[IbrahimIjai]

Context

Documentation 404s come from renamed pages and from links pasted years ago. A
bare "not found" wastes that visit; suggesting the closest existing page usually
recovers it.

Scope

• A 404 page that keeps the sidebar and search available.
• Suggest the closest matching pages from the requested path using string
  distance over the page index, capped at a few suggestions and only when the
  match is reasonable.
• Offer the search dialog prefilled with terms from the path.
• Link to the section index that the path implies, when one exists.
• Return a real 404 status, not a 200 with 404 content.

Acceptance criteria

• The response status is 404, verified against the built output.
• A renamed-page path suggests the new page.
• A nonsense path shows no misleading suggestions.
• Search and sidebar remain functional on the 404 page.

Out of scope

• Server-side logging of 404s.

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Spec: docs/dx_1/001_docs_site.md · Depends on: DX-048

[razeprasine]

@razeprasine has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi maintainer, I would love to fix this

ℹ️ Repo Maintainers: To accept this application, review their application or assign @razeprasine to this issue.

[drips-wave]

Congratulations, @razeprasine! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

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