The terminal looked soft/heavy on every platform because the xterm
Terminal was built with allowTransparency: true, which drops the WebGL
renderer's opaque fast-path and bakes glyphs as grayscale-alpha coverage
for compositing over a see-through canvas. Our surface (--ui-bg-chrome)
is opaque and withSurface already paints it, so transparency was pure
blur for no benefit — VS Code keeps it off too. Also drop the Medium
(500) base weight for normal/bold (400/700) to match VS Code's metrics,
and remove the now-unused JetBrains Mono Medium face + woff2.
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