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>

hosts/ocaml/browser/sx_browser.ml

@@ -684,6 +684,34 @@ let () =
   ignore (env_bind global_env "VOID_ELEMENTS" void_elements);
   ignore (env_bind global_env "BOOLEAN_ATTRS" boolean_attrs);
 
+  (* --- HTML tag special forms (div, span, h1, ...) --- *)
+  (* Registered as custom special forms so keywords are preserved.
+     Handler receives (raw-args env), evaluates non-keyword args
+     while keeping keyword names intact. *)
+  let eval_tag_args raw_args env =
+    let args = Sx_runtime.sx_to_list raw_args in
+    let rec process = function
+      | [] -> []
+      | (Keyword _ as kw) :: value :: rest ->
+        (* keyword + its value: keep keyword, evaluate value *)
+        kw :: Sx_ref.eval_expr value env :: process rest
+      | (Keyword _ as kw) :: [] ->
+        (* trailing keyword with no value — boolean attr *)
+        [kw]
+      | expr :: rest ->
+        (* non-keyword: evaluate *)
+        Sx_ref.eval_expr expr env :: process rest
+    in
+    process args
+  in
+  List.iter (fun tag ->
+    ignore (Sx_ref.register_special_form (String tag)
+      (NativeFn ("sf:" ^ tag, fun handler_args ->
+        match handler_args with
+        | [raw_args; env] -> List (Symbol tag :: eval_tag_args raw_args env)
+        | _ -> Nil)))
+  ) Sx_render.html_tags;
+
   (* --- Error handling --- *)
   bind "cek-try" (fun args ->
     match args with