Replace the single-pass guillotine split approach with RemnantFinder-based
iteration. After each fill, re-discover all free rectangles and try all
remaining items again until no more progress is made. This fills gaps that
were previously left empty after the initial strip + remainder layout.
Also change ActiveWorkArea border color from orange to red.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>