Replace charmap's hand-drawn scrollbar with the mtk scrollbar widgets
(scrollbar_track_rect / scrollbar_thumb_rect / draw_scrollbar), matching the
Devices and Music apps: standard 12px track colored SCROLLBAR_BG/FG with a
draggable thumb. Adds thumb drag, track-click-to-jump, and hover highlight
(mirroring devexplorer's handling); the tile grid reserves an SB_GUTTER on the
right sized from mtk::SCROLLBAR_W. The bar auto-hides when the set fits.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
daniel
743eca2051