fix: sitemap issues and deduplicate

[flatsponge]

Summary

Fix sitemap so search engines and AI agents can reliably consume
https://ethereum.org/sitemap.xml again.
Closes #17260

What changed

• Restored homepage inclusion in sitemap (/ for default locale).
• Added dynamic /developers/tools/[category]/ routes to sitemap generation (all 7 category
  pages).
• Removed unreliable sitemap fields:
  • lastModified (previously deploy-time for every URL)
  • changeFrequency
  • priority
• Added sitemap hreflang alternates via alternates.languages, including x-default.
• Fixed translation namespace matching for /developers/tools/* to use the correct namespace
  (page-developers-tools).

Why

• Homepage and live tools category pages were missing from sitemap output.
• Uniform deploy-time lastModified made freshness metadata untrustworthy.
• No sitemap hreflang alternates reduced multilingual discoverability.
• Namespace fallback for tools routes could produce incorrect translated-locale detection.

[netlify]

✅ Deploy Preview for ethereumorg ready!

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🔨 Latest commit	bbcc554
🔍 Latest deploy log	https://app.netlify.com/projects/ethereumorg/deploys/69b0b88eaac6300008c21ca7
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Lighthouse	7 paths audited Performance: 60 (🟢 up 7 from production) Accessibility: 94 (🟢 up 1 from production) Best Practices: 100 (no change from production) SEO: 99 (no change from production) PWA: 59 (no change from production) View the detailed breakdown and full score reports

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[myelinated-wackerow]

Well-researched PR that addresses all 5 issues from #17260. A few notes:

Build is failing — deploy preview didn't make it. Worth investigating before further review. Could be the new import of DEV_TOOL_CATEGORY_SLUG_LIST from the data-layer into translationRegistry.ts introducing a build-order or circular dependency issue.

hreflang locale filtering may be too restrictive: isLocaleValidISO639_1 filters the alternates list, but hreflang supports BCP 47 tags (e.g., zh-TW, pt-BR), not just ISO 639-1. Regional locales like zh-tw and pt-br would appear in sitemap URLs but be absent from the alternates.languages block. Worth confirming this is intentional.

The dedup approach is cleaner than the old hack — replacing the homepage-specific skip with a generic seenUrls Set is the right call. Removing the unreliable lastModified/priority/changeFrequency fields is also correct per Google's own docs.

Overlap note: PR #17563 addresses a subset of this (homepage only) with a simpler hardcoded approach. This PR supersedes it entirely if the build gets fixed.

Please fix the build and we can take another look.

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🤖 Reviewed by Claude / claude-opus-4-6

[flatsponge]

should be fixed now! thank you for the quick review! :)

[myelinated-wackerow]

Thanks @flatsponge! Appreciate the fixes.

Approving this PR. We've merged the latest dev into this branch -- just waiting on the Netlify build to confirm everything is still green before merging.

Verification against the deploy preview sitemap:

• Homepage (/) is present with full hreflang alternates including x-default
• All 7 /developers/tools/[category]/ pages are present with locale variants
• hreflang alternates use proper BCP 47 tags (pt-br, zh-tw correctly included)
• lastModified, changeFrequency, and priority fields are fully removed (Google ignores these anyway)
• No duplicate /en/ root entry -- the seenUrls dedup works correctly
• URL count is ~6,614 vs production's ~6,857 -- the decrease is expected from deduplication of default-locale entries

Architecture notes:

• The shared src/data/developerTools.ts as single source of truth for category slugs is a clean refactor
• The /developers/tools/ namespace mapping addition in translations.ts fixes locale detection for those routes
• Removing the isLocaleValidISO639_1 filter from metadata.ts is correct -- hreflang supports BCP 47, not just ISO 639-1

This PR supersedes #17563 and #17567 -- both can be closed once this merges.

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Reviewed by Claude / claude-opus-4-6

[wackerow]

@all-contributors add @flatsponge for code

[allcontributors]

@wackerow

@flatsponge already contributed before to code