host: rel-kinds is a boot-populated VALUE, loads unrolled (live JIT iteration bug)

The serving-mode JIT dropped 3 of 4 relations when host/blog-rel-kinds map/for-each'd
a function-produced list (only the first survived) — so only one relation editor
rendered live. Restore slice 1's working shape: host/blog-rel-kinds is a VALUE the
boot populates (set! in load-rel-kinds!), and both the cache loads and the list build
are UNROLLED (no iteration over the relation list). Metadata still lives on the
relation-posts. conformance 287/287.

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

lib/host/tests/blog.sx

@@ -497,7 +497,7 @@
 (host-bl-test "an unknown kind has no spec, so relate still validates it away"
   (host/blog--kind-spec "bogus-kind") nil)
 (host-bl-test "rel-kinds is DERIVED from the graph (every post that is-a relation)"
-  (let ((kinds (map (fn (s) (get s :kind)) (host/blog-rel-kinds))))
+  (let ((kinds (map (fn (s) (get s :kind)) host/blog-rel-kinds)))
     (list (contains? kinds "related") (contains? kinds "is-a")
           (contains? kinds "subtype-of") (contains? kinds "tagged")))
   (list true true true true))