Adds the library infrastructure without visible change to the rendered
page: a 'featured:' list in each portal's tag-meta sidecar drives shelf
curation (up to 5, default cap 4, recency fills the rest), a content/
library.md snapshot feeds a '\$library-intro\$' slot for a leading
blockquote, and '\$<slug>-has-more\$' gates expose whether the unfiltered
portal overflows the shelf. Items are now loaded once and partitioned
by primary portal rather than scanned per-section.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
