Makes the Craft.js editor usable on phones (≤768px) without touching desktop
layout/behavior: a useIsMobile() hook gates a bottom tab bar + sheets (hosting
the existing Blocks/Pages/Layers/Assets/Styles panels unchanged) in place of
the side panels, a collapsed TopBar with a "..." overflow menu, 44px touch
targets, 16px inputs, dvh/safe-area-aware sizing, and small copy/overflow
fixes (empty-canvas hint, Templates modal tabs + close button).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
