Add DOMContentLoaded, load, and readystatechange events with correct
readyState transitions (loading→interactive→complete). Includes Window
as a first-class event target, body onload spec quirk, and idempotency
guards to prevent double-firing. Code review hardened the API surface
by enforcing forward-only state transitions, eliminating a redundant
wrapper function, and requesting a redraw after load handler DOM mutations.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
626a1c517c