The fallback extension icon now has a transparent background, matching the light/dark theme variants already in the manifest. Cosmetic consistency fix — no functional change.
What shipped
•icon.png (fallback used when a client doesn't honour the light/dark icon variants) was an opaque black square. Replaced with the transparent-black variant so the fallback also renders cleanly. The existing icon-light.png (transparent black) and icon-dark.png (transparent white) variants were already correct.