Why pack_product.py uses fixed 1280x720 covers and 600x600 thumbnails

The author lost hours to a product cover that rendered at an arbitrary size and looked distorted on marketplace listings, which prompted explicit sizing in the pack_product.py script. The 16:9 cover at 1280x720 suits most link previews and product pages, and it renders quickly and within memory limits on a small 1 vCPU, 2 GB server. The square 600x600 thumbnail fits marketplace tiles without cropping, and it has its own text layout rather than a cropped resize of the cover. The script zips the product, renders both images, and writes all outputs in one run to keep them consistent across updates.