host: style the /new editor — inline sx-editor styles via render-page

The editor was unstyled: editor.css is .koenig-lexical-scoped (the OTHER editor);
the sx-editor's .sx-* styles live in the ~editor/sx-editor-styles component
(inline <style> in blog/sx/editor.sx). Inline them into /new by rendering that
component with the 5.1 render-page primitive (dogfooding the capability live), +
FontAwesome for the +/slash-menu icons. 79 .sx- rules now inlined.

Also: the sx_host container only mounted spec+lib, so web/adapter-html.sx (and
now blog/sx/{layouts,editor}.sx) silently failed to load at boot -> render-page
errored -> /new 502. Mount ./web + ./blog (ro) so they load. (Transitional reuse
of the legacy blog editor component + its styles; retire via the asset-manifest +
native SX-island editor.)

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

docker-compose.dev-sx-host.yml

@@ -27,6 +27,10 @@ services:
       # SX source (hot-reload on container restart)
       - ./spec:/app/spec:ro
       - ./lib:/app/lib:ro
+      - ./web:/app/web:ro
+      # blog app SX — reused for the editor's style component (transitional;
+      # retire when the editor + its styles are host-owned / asset-managed)
+      - ./blog:/app/blog:ro
       # OCaml server binary — this worktree's build (has the SX_HTTP_HOST bind fix)
       - ./hosts/ocaml/_build/default/bin/sx_server.exe:/app/bin/sx_server:ro
       # Durable persist store (the SX op-log/kv on disk) — survives restarts.