Fix broken links in versioned docs

[ewgenius]

Older documentation versions (<= 1.9.x) still contain broken links.
In #1367, the build configuration was modified to disable build failures and unblock docs publishing.

Need to fix the documentation for all versions and re-enable link validation.

[claudespice]

Verified this is resolved:

• Build config: website/docusaurus.config.ts now has onBrokenLinks: 'throw', onBrokenAnchors: 'throw', and onBrokenMarkdownLinks: 'throw' (lines 111–117) — strict link checking is active on trunk.
• Resolved by commit 4f686ba8 "Enable strict broken link checking in Docusaurus build" (2026-02-05), followed by 78028929 "Fix broken links" and 027a45a7 "Re-enable throw" (2026-02-15), which re-enabled strict handling after Change broken link and anchor handling to warn instead of throw #1367 temporarily relaxed it.
• Live site: https://docs.spiceai.org builds cleanly with the stricter settings across all versioned directories (version-1.5.x through version-1.11.x).

Closing as fixed. Please reopen if a broken link resurfaces in any versioned doc.