HS: halt command modes, mock event methods

Parser:
- halt default/bubbling: match ident type (not just keyword)
- halt the event's: consume possessive marker

Runtime:
- hs-halt! dispatches: default→preventDefault, bubbling→stopPropagation,
  event→both

Mock DOM:
- Add event method dispatch: preventDefault, stopPropagation,
  stopImmediatePropagation set correct flags on event dict

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

hosts/ocaml/bin/run_tests.ml

@@ -1807,6 +1807,15 @@ let run_spec_tests env test_files =
             | _ -> Bool false)
          | _ -> Nil)
 
+      else if mt = "event" then
+        (match m with
+         | "preventDefault" -> Hashtbl.replace d "defaultPrevented" (Bool true); Nil
+         | "stopPropagation" -> Hashtbl.replace d "_stopped" (Bool true); Nil
+         | "stopImmediatePropagation" ->
+           Hashtbl.replace d "_stopped" (Bool true);
+           Hashtbl.replace d "_stopImmediate" (Bool true); Nil
+         | _ -> Nil)
+
       else if mt = "style" then
         (match m with
          | "setProperty" ->