Add W/H inputs, aspect-ratio lock, resampling method dropdown (nearest /
bilinear / box), "Fit to canvas" (respects current origin) and "1:1" reset
buttons to the import panel. Pipeline now runs resize before palette
quantization so dither/skip-matching operate on the final dimensions.
Shared src/lib/image-resize.js is reused by scripts/image-to-colors.js,
which gains --width, --height, --method flags with aspect-preserve when
only one dimension is provided.
