OCaml raw! in HTML renderer + SX_USE_OCAML env promotion + golden tests

- sx_render.ml: add raw! handler to HTML renderer (inject pre-rendered
  content without HTML escaping)
- docker-compose.yml: move SX_USE_OCAML/SX_OCAML_BIN to shared env
  (available to all services, not just sx_docs)
- hosts/ocaml/Dockerfile: OCaml kernel build stage
- shared/sx/tests/: golden test data + generator for OCaml render tests

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docker-compose.yml

@@ -58,6 +58,8 @@ x-app-env: &app-env
   EXTERNAL_INBOXES: "artdag|https://celery-artdag.rose-ash.com/inbox"
   SX_BOUNDARY_STRICT: "1"
   SX_USE_REF: "1"
+  SX_USE_OCAML: "1"
+  SX_OCAML_BIN: "/app/bin/sx_server"
 
 services:
   blog:
@@ -228,8 +230,6 @@ services:
       <<: *app-env
       REDIS_URL: redis://redis:6379/10
       WORKERS: "1"
-      SX_USE_OCAML: "1"
-      SX_OCAML_BIN: "/app/bin/sx_server"
 
   db:
     image: postgres:16