Fix source display: add sxc mount, HTML tag forms, Playwright debug tools

- Add missing ./sx/sxc:/app/sxc:ro volume mount to dev-sx compose —
  container was using stale image copy of docs.sx where ~docs/code had
  (&key code) instead of (&key src), so highlight output was silently
  discarded
- Register HTML tags as special forms in WASM browser kernel so keyword
  attrs are preserved during render-to-dom
- Add trace-boot, hydrate-debug, eval-at modes to sx-inspect.js for
  debugging boot phases and island hydration

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

docker-compose.dev-sx.yml

@@ -17,6 +17,7 @@ services:
       - ./lib:/app/lib:ro
       - ./web:/app/web:ro
       - ./sx/sx:/app/sx:ro
+      - ./sx/sxc:/app/sxc:ro
       - ./shared:/app/shared:ro
       # OCaml binary (rebuild with: cd hosts/ocaml && eval $(opam env) && dune build)
       - ./hosts/ocaml/_build/default/bin/sx_server.exe:/app/bin/sx_server:ro