Corners were drawn by two disagreeing algorithms: a hand-rolled per-row inset for
the gradient fill and TFT_eSPI's Bresenham arc for the border, so they missed each
other by a pixel and left a halo. The inset was also wrong, truncating the sqrt and
ignoring pixel centres, which over-cut the top row by 2px into a visible chamfer.
gui.roundRect now derives fill and border from the same signed distance, blending
edge pixels by coverage, and replaces fillRoundRect, drawRoundRect and
fillRectGradient. The geometry moved to src/gfx/round_rect.h so round_rect_test.cpp
can check the arc on the host, since only the eye ever checked the old one.
evan
36953bb140