feat(screenshots): add 13" iPad App Store screenshot support

Fix hero compositor being phone-only (hardcoded 19.5:9 aspect + Dynamic
Island chrome squeezed the iPad screenshot into a cropped phone-shaped
sliver); derive aspect ratio from the actual device and add tablet
chrome. Fix iOS output filenames colliding across device sizes since
deliver globs screenshots flat per locale dir. Rename existing iPhone
6.9" screenshots to include the device suffix and add the iPad 13" set.

Author: F2had