Stop adding a transparent inset to full-bleed macOS app icons

Apps built for macOS show a Dock icon that is smaller than other apps' icons, with a thin transparent gap — the desktop wallpaper shows through between the artwork and the edge of the icon tile, so the icon looks shrunken and slightly floating.

Studio currently scales a square, full-bleed app icon down to about 88% of the icon canvas and surrounds it with a transparent margin before generating the .icns file. Modern macOS expects square artwork that runs edge to edge and applies the rounded corners itself, so that margin is rendered as empty space inside the Dock tile.

Expected behaviour: a full-bleed square PNG fills the icon tile edge to edge, matching every other macOS app. Non-square images will still be centred on a square canvas without distortion so they are not stretched. The expected icon format (square, full-bleed, no padding, no pre-rounded corners) will be documented alongside the fix.