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>

lib/hyperscript/runtime.sx

@@ -222,8 +222,13 @@
     (mode)
     (when
       event
-      (host-call event "preventDefault" (list))
-      (when (= mode "event") (host-call event "stopPropagation" (list))))))
+      (cond
+        ((= mode "default") (host-call event "preventDefault"))
+        ((= mode "bubbling") (host-call event "stopPropagation"))
+        (true
+          (do
+            (host-call event "preventDefault")
+            (host-call event "stopPropagation")))))))
 
 ;; ── Type coercion ───────────────────────────────────────────────