docs: article contract gains embeds — build-time code from…

docs: article contract gains embeds — build-time code from git.nech.pl/github/raw, directive islands

DESIGN.md

@@ -78,6 +78,11 @@ project badges. Prose-forward, scannable.
   lightbox on click
 - language switch on the article itself, remembers choice; untranslated posts say so honestly
 - search-to-section and load-page-with-highlight-text-to-match (gwern-grade UX)
+- **Embedded media, first-class:** stellar code blocks sourced from git.nech.pl, GitHub, or
+  raw URLs — fetched at build time, pinned to SHA, shiki-highlighted at build, with a source
+  permalink (and tabs for multi-file); plus directive islands for basic animations, dynamic
+  interactive sections, and Hydra items. Build-time fetching keeps the no-third-party-calls
+  rule intact: the reader's browser never phones out; everything bakes into static HTML.
   > *"oh yes inspiration is gwen.net ofc also, with stellar notes experience, with asides
   > rendered inside on desktop, proper on mobile, etc. search to section,
 > load-page-wtih-highlight-text-to-match, etc stellar UX"*