Applying display:flex to both html and body caused body to shrink-wrap
as a flex item of html, making cells ~53px instead of ~102px. Split the
rule so only body gets the flex centering. Also measure actual cell size
synchronously after initUI mounts and use it for tile translate calculations
so tiles align correctly regardless of container width.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>