Add StrongTypes intervals blog post + surface Interval types on the strong-types page

[KaliCZ]

What

Documents the interval types shipped in Kalicz.StrongTypes v1.2.0, in two places:

1. New bilingual blog post — Type-Safe Intervals in Your .NET API (type-safe-intervals-in-your-dotnet-api). It is a follow-up to the zero-code validations post (linked at the top, alongside the StrongTypes page), and picks up the Interval<T> teaser from the end of that article. It uses a subscription-membership story to walk through:

   • a start/end pair that can silently go backwards, and the checks that leak into every layer as a result;
   • FiniteInterval<DateOnly> validating the ordering once, at construction;
   • Contains / Overlaps for the functionality you would otherwise hand-roll and test;
   • the four variants (Interval, FiniteInterval, IntervalFrom, IntervalUntil);
   • JSON serialization on the API boundary; and
   • EF Core endpoint-column mapping, so "every membership running longer than 30 days, email them a renewal offer" is just a SQL-translated query.

2. strong-types page — the Validated wrappers feature group is renamed to Validated types, and the Interval<T> family is added to it (EN + CS).

Notable details

• Registered the post's slug in BlogPostCatalog with a fresh, permanent comment-stream Guid so reactions/comments resolve; the all-posts anti-drift E2E would otherwise fail. Extended BlogPostCatalogTests to cover it.
• Bumped the strong-types page updatedDate so its sitemap lastmod reflects the change.
• No em dashes; personal first-person voice, mirroring the sibling post's structure and wording.

Testing

• astro build — passes; both /blog/... and /cs/blog/... routes plus RSS and sitemap generate cleanly.
• dotnet test on Kalandra.Blog.Tests — 33 passing.
• The full suite (integration + Playwright + E2E, which need Docker/Supabase/Temporal) is left to CI.

🤖 Generated with Claude Code