[Dicey Tales] Downscale WEBP images to display size

Resize all 29 WEBP images to 2x their on-screen dimensions (from
their original PNG sources, preserving alpha) so the sheet loads fast
in Roll20. Total payload drops from ~3.1 MB to ~485 KB; the largest
offenders (logo 1.3 MB -> 31 KB, background 734 KB -> 161 KB) were
huge oversized source files scaled down.