feat: generate product comparison pages for curated products

[514sid]

What

Adds auto-generated 1-to-1 comparison pages (/compare/{a}-vs-{b}/) for a curated set of notable products, built entirely at Hugo build time from existing product data.

• A Hugo content adapter (content/compare/_content.gotmpl) emits one page per unordered pair of products that appear in the allowlist AND share a category. Comparisons never cross categories (no CMS vs Content provider).
• The allowlist lives in data/compare.yaml (53 products), so the set is explicit and easy to curate. Current output: 1,378 pages.
• Each page has a generated SEO intro, side-by-side logo cards, and a spec table (category, HQ, founded, platforms, open source, self-signup, API, docs) pulled live from each product's data, so pages are differentiated rather than thin.
• Product pages for allowlisted products gain a "Compare {name} with" section linking to every same-category peer, so the comparison pages are internally linked and crawlable.
• No /compare/ landing page is rendered (build.render: never on the section).

Why a curated allowlist

Full pairwise across all ~600 products is ~171,000 pages / ~9 GB, which exceeds the GitHub Pages 1 GB serving limit and would overflow a single sitemap. The allowlist keeps the set to recognizable products buyers actually shortlist: ~50 products is the sweet spot (page count grows as n(n-1)/2 within a category). The list is trivial to extend by editing data/compare.yaml.

SEO

• Unique <title>, meta description, canonical, and OG/Twitter tags per page via the existing head.html.
• Comparison pages enter the sitemap; 1,378 URLs stays well under the 50k single-file limit.

Files

• content/compare/_content.gotmpl - pair generator (allowlist + same-category)
• content/compare/_index.md - section set to never render
• layouts/compare/single.html - comparison layout with generated SEO text
• data/compare.yaml - curated product allowlist
• layouts/products/single.html - "Compare with" links on allowlisted pages
• content/updates/2026-07-27.md - changelog entry

Notes

• Impact is scoped: only the 53 allowlisted product pages change; the other ~570 render identically.
• Full build with comparisons runs in ~1.6s and adds ~15 MB to public/.