Hyperscript examples working: toggle, bounce, count clicks

- sx_browser.ml: restore VmSuspended handler in api_call_fn with
  make_js_callFn_suspension for IO suspension chains (wait, fetch)
- runtime.sx: delete host-get stub that shadowed platform native —
  hs-toggle-class! now uses real FFI host-get for classList access

All three live demo examples work:
  Toggle Color — classList.toggle on click
  Bounce — add .animate-bounce, wait 1s suspend, remove
  Count Clicks — increment @data-count, put into innerHTML

4/4 bytecode regression tests pass (was 0/4 without VmSuspended).

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

hosts/ocaml/browser/sx_browser.ml

@@ -487,12 +487,35 @@ let api_register_native name_js callback_js =
   Hashtbl.replace _vm_globals name v;
   Js.Unsafe.inject Js.null
 
+let rec make_js_callFn_suspension request vm =
+  let obj = Js.Unsafe.obj [||] in
+  Js.Unsafe.set obj (Js.string "suspended") (Js.Unsafe.inject Js._true);
+  Js.Unsafe.set obj (Js.string "request") (value_to_js request);
+  Js.Unsafe.set obj (Js.string "resume") (Js.wrap_callback (fun result_js ->
+    let result = js_to_value result_js in
+    try
+      let v = Sx_vm.resume_vm vm result in
+      sync_vm_to_env ();
+      value_to_js v
+    with
+    | Sx_vm.VmSuspended (req2, vm2) ->
+      Js.Unsafe.inject (make_js_callFn_suspension req2 vm2)
+    | Eval_error msg ->
+      ignore (Js.Unsafe.meth_call
+        (Js.Unsafe.get Js.Unsafe.global (Js.string "console"))
+        "error" [| Js.Unsafe.inject (Js.string ("[sx] resume: " ^ msg)) |]);
+      Js.Unsafe.inject Js.null));
+  obj
+
 let api_call_fn fn_js args_js =
   try
     let fn = js_to_value fn_js in
     let args = Array.to_list (Array.map js_to_value (Js.to_array (Js.Unsafe.coerce args_js))) in
     return_via_side_channel (value_to_js (call_sx_fn fn args))
   with
+  | Sx_vm.VmSuspended (request, vm) ->
+    sync_vm_to_env ();
+    Js.Unsafe.inject (make_js_callFn_suspension request vm)
   | Eval_error msg ->
     ignore (Js.Unsafe.meth_call
       (Js.Unsafe.get Js.Unsafe.global (Js.string "console"))