renderBuffBar is ~400 lines and the layout maths was buried in the middle of it,
which is exactly where a silent bug lives: the row does not wrap, so it has a hard
capacity, and it has to stay clear of the minimap at every resolution and scale.
The arithmetic moves to buff_bar_layout.hpp as a pure function and combat_ui.cpp
calls it, so the tested maths is the maths that runs. 408 assertions sweep
resolutions from 1280x720 to 4K and scales from 0.75x to 1.5x, checking the row
never overlaps the minimap, never runs off screen, drops overflow rather than
wrapping, and always gives weapon enchants their slots before auras.
