feat: add biweekly contest 154

[yanglbme]

No description provided.

[idoocs]

Images automagically compressed by Calibre's image-actions ✨

Compression reduced images by 46.1%, saving 74.94 KB.

Filename	Before	After	Improvement	Visual comparison
solution/3500-3599/3515.Shortest Path in a Weighted Tree/images/1744423806-WSWbOq-screenshot-2025-03-13-at-133306.png	31.08 KB	17.72 KB	-43.0%	View diff
solution/3500-3599/3515.Shortest Path in a Weighted Tree/images/1744423814-SDrlUl-screenshot-2025-03-13-at-133524.png	30.29 KB	16.20 KB	-46.5%	View diff
solution/3500-3599/3515.Shortest Path in a Weighted Tree/images/1744423824-zZqYvM-screenshot-2025-03-13-at-132247.png	19.86 KB	9.83 KB	-50.5%	View diff
solution/3500-3599/3515.Shortest Path in a Weighted Tree/images/screenshot-2025-03-13-at-132247.png	19.86 KB	9.83 KB	-50.5%	View diff
solution/3500-3599/3515.Shortest Path in a Weighted Tree/images/screenshot-2025-03-13-at-133306.png	31.08 KB	17.72 KB	-43.0%	View diff
solution/3500-3599/3515.Shortest Path in a Weighted Tree/images/screenshot-2025-03-13-at-133524.png	30.29 KB	16.20 KB	-46.5%	View diff

2046 images did not require optimisation.