The mobile hamburger is a <div class="mobile-menu-icon"> with a click
handler, so it worked on tap but was invisible to keyboard and screen-reader
users. Expose it as a button in main.js: role="button", tabindex="0",
aria-label, aria-expanded toggling, and Enter/Space activation. Verified in
a headless browser (focusable, Enter opens, aria state flips).
Also adds docs/PRE-LAUNCH-CHECKLIST.md (dev-only, excluded from deploy):
inventory of remaining content placeholders for the public launch.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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