electron-builder was given a single 2048x2048 icon.png and dumped it into
hicolor/2048x2048/apps/, a bucket no Linux desktop environment indexes —
launchers and taskbar fell back to a generic placeholder. Pre-render the
standard sizes (16, 32, 48, 64, 128, 256, 512, 1024) and point linux.icon
at the directory so each PNG lands in the matching hicolor/NxN/apps/ slot.
Tray icon was unaffected (loaded at runtime via Electron's Tray API from
bundled resources, no theme lookup).
