host: Phase 5.1 — interactive SX-page render from a handler, 181/181

KERNEL: add a render-page primitive (sx_server.ml, persistent mode) that renders
an UNEVALUATED SX expression with the server env via sx_render_to_html.
render-to-html expands defcomp components and collects keyword attrs itself; SX
handlers can't reach the server env, so the prim supplies it. Fixes the attr
mangling — bare render-to-html on an EVALUATED component tree turns (form :id ..)
into <form>idpost-new-form..; rendering the unevaluated expr keeps :id an attr.

HOST: lib/host/page.sx — host/page (expr -> HTML response) + host/page-route
(mount on a GET path). New page suite (8 tests) proves a generic attributed +
nested component renders correctly through a host route; verified ~editor/form
renders right too. This is the component-render step of the generic
interactive-SX-page capability; shell + static assets + hydration (5.2-5.4) next.

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

lib/host/conformance.sh

@@ -76,6 +76,7 @@ MODULES=(
   "lib/host/feed.sx"
   "lib/host/relations.sx"
   "lib/host/blog.sx"
+  "lib/host/page.sx"
   "lib/host/server.sx"
   "lib/host/ledger.sx"
 )
@@ -89,6 +90,7 @@ SUITES=(
   "feed        host-fd-tests-run!  lib/host/tests/feed.sx"
   "relations   host-rl-tests-run!  lib/host/tests/relations.sx"
   "blog        host-bl-tests-run!  lib/host/tests/blog.sx"
+  "page        host-pg-tests-run!  lib/host/tests/page.sx"
   "server      host-sv-tests-run!  lib/host/tests/server.sx"
   "ledger      host-lg-tests-run!  lib/host/tests/ledger.sx"
 )