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>

shared/sx/ocaml_bridge.py

@@ -401,7 +401,7 @@ class OcamlBridge:
             # signals.sx provides reactive primitives for island SSR)
             web_dir = os.path.join(os.path.dirname(__file__), "../../web")
             if os.path.isdir(web_dir):
-                for web_file in ["signals.sx", "adapter-sx.sx"]:
+                for web_file in ["signals.sx", "adapter-html.sx", "adapter-sx.sx"]:
                     path = os.path.normpath(os.path.join(web_dir, web_file))
                     if os.path.isfile(path):
                         all_files.append(path)