host: live 2-field composition demo (Landing type: :body + :aside)

host/blog-seed-landing-demo! (+ host/blog--seed-card! fixed-slug helper): a Landing TYPE with
TWO composition fields — :body (heading/text/image + cond/each) and :aside (text/callout, no
controls) — plus a populated landing-demo instance, wired into serve.sh (survives wipes),
idempotent (fixed card slugs, set-comp! overwrites). /landing-demo/ renders both fields; its
edit page shows two independent block editors (#comp-body, #comp-aside); /landing/ reads the
two-field definition. Demonstrates layer 2 end to end on the live site.

blog 196/196 (+ tests: idempotent 2-field seed, both fields render).

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

lib/host/serve.sh

@@ -169,6 +169,11 @@ EPOCH=1
   echo "(epoch $EPOCH)"
   echo "(eval \"(host/blog-seed-nt-live-encore!)\")"
   EPOCH=$((EPOCH+1))
+  # Seed the layer-2 demo: a Landing type with TWO composition fields (:body + :aside) + a
+  # populated instance — so the two-field composition editor + render show side by side.
+  echo "(epoch $EPOCH)"
+  echo "(eval \"(host/blog-seed-landing-demo!)\")"
+  EPOCH=$((EPOCH+1))
   # Load relation metadata (symmetry/labels) from the relation-posts into the
   # in-memory cache, so render paths read it without a (VmSuspending) durable read.
   echo "(epoch $EPOCH)"