Replace vaxis NewImage/Resize (which spawns goroutines that panic in
sixel encoder) with direct halfblock character rendering. Each terminal
cell uses upper-half-block with RGB fg/bg colors for 2x vertical
resolution. Pre-renders in background goroutine, Draw() just paints
pre-computed cells. Works in any 24-bit color terminal.
Mortdecai
8a19e0b95c