Island SSR: defislands render to HTML server-side with hydration markers

Islands now render their initial state as HTML on the server, like
React SSR. The client hydrates with reactive behavior on boot.

Root causes fixed:
- is_signal/signal_value now recognize Dict-based signals (from
  signals.sx) in addition to native Signal values
- Register "context" as a primitive so the CEK deref frame handler
  can read scope stacks for reactive tracking
- Load adapter-html.sx into kernel for SX-level render-to-html
  (islands use this instead of the OCaml render module)
- Component accessors (params, body, has-children?, affinity) handle
  Island values with ? suffix aliases
- Add platform primitives: make-raw-html, raw-html-content,
  empty-dict?, for-each-indexed, cek-call

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

docker-compose.dev-sx.yml

@@ -17,6 +17,7 @@ services:
       SX_OCAML_BIN: "/app/bin/sx_server"
       SX_BOUNDARY_STRICT: "1"
       SX_DEV: "1"
+      OCAMLRUNPARAM: "b"
     ports:
       - "8013:8000"
     volumes: