v0.87.0: fragments — reusable content, authored once and included anywhere

Fragments: author one piece of markdown, include it anywhere, edit it once. A site declares the
reserved fragments concept, and an editor inserts a published fragment into any post or page
with the "Include a fragment" picker; the fragment's markdown splices in as a block, renames
repoint every inbound include, and deleting a still-included fragment is refused with its
consumers named. New guide: Reuse content across
entries.

The window also clears the docs friction log end to end: every open finding was verified against
the code and either shipped here or filed into ROADMAP with its trigger.

Changed

• A routing: 'embedded' concept is now genuinely non-routable: its entries no longer resolve
  through byPermalink, prerender through entries(), or appear in site.all(). Consumers
  must: check any concept declared routing: 'embedded'. If its entries should have public
  URLs, declare routing: 'page' instead; if they only ever served as references or includes,
  nothing to do, and the stray URLs stop being served. Neither ecxc.ski nor 907.life declares an
  embedded concept.

Added

• Fragments (above), including the ::include block directive, the picker, the manifest
  includes edge, the delete guard, rename repointing, and the fragment edit screen's standing
  "Included in" list.
• Folded directive blocks name themselves: the fold pill reads "Callout · 12 lines" from the
  component registry's human label and carries the component's use line as its tooltip; an
  ::include line renders its fragment id at label strength.
• SettingsData and VocabularyLoadData are exported from @glw907/cairn-cms/sveltekit.
• A configured AuthBranding.replyTo now reaches the built-in magic-link email.

Fixed

• Saving Tidy settings or the tag vocabulary over a malformed committed site config surfaces the
  parser's actionable message instead of a generic error page.
• A required closed multiselect signals "Choose at least one." through the browser's own
  validation instead of failing only at the save bounce.
• The suggestion popover styles a backtick-quoted word as code; help hints in repeated rows get
  distinct ids; and three fragments papercuts from an adversarial UX review (the list delete
  refusal's copy, the picker's empty state, the nameless-include notice).

Full detail: CHANGELOG.