host: load kg-cards components so imported Ghost posts render fully

Imported Ghost posts' sx_content holds (~kg_cards/kg-*) (from the lexical_to_sx converter);
the host's render-page resolves components, but the kg-cards weren't loaded so they
degraded to '(unsupported block)' placeholders. Copied blog/sx/kg_cards.sx ->
lib/host/sx/kg-cards.sx (host self-contained, not coupled to the legacy blog/ Quart dir)
+ added the one host-local dep ~rich-text (was only a test fixture) + registered it in
serve.sh + conformance.sh module lists. Verified: the real 'Free DVD Box Sets!' post now
renders <figure class=kg-card kg-image-card> for all images, zero placeholders.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/host/serve.sh

@@ -83,6 +83,7 @@ MODULES=(
   "lib/host/router.sx"
   "lib/host/static.sx"
   "lib/host/sx/relate-picker.sx"
+  "lib/host/sx/kg-cards.sx"
   "lib/host/feed.sx"
   "lib/host/relations.sx"
   "lib/host/blog.sx"