Implements the W3C DOM event model connecting JavaScript event handlers to the DOM tree with full capture/target/bubble phase propagation. - Event constructor: new Event(type, options) with bubbles/cancelable - Event methods: preventDefault, stopPropagation, stopImmediatePropagation - EventTarget methods on all node wrappers and document: addEventListener, removeEventListener, dispatchEvent - Event propagation: capture phase -> at-target -> bubble phase - Support for capture option (boolean or options object) - Support for once option (auto-remove after first invocation) - Event listener GcRefs registered as GC roots - 20 new tests covering all acceptance criteria Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>