PR #171 made relayoutCanvas() set canvas.style.width/height
explicitly, but the canvas is a flex item: flex items default to
min-width/min-height: auto, which resolves to the canvas's intrinsic
framebuffer resolution and clamps the JS-set display size right back
up to native — so fit mode still did nothing (#133, "still same
behavior").
Add min-width/min-height: 0 (+ flex: none) on the canvas in fit mode
so the explicit downscaled size actually sticks. Scoped to
#canvas-wrap.fit so non-fit mode keeps native size + scroll.
re #133
4814aaefdb