Generate build/icon.svg — a white download glyph on the teal brand square,
mirroring the in-app brand mark (Onboarding.tsx) — and rasterise it to a
multi-size build/icon.ico (256/128/64/48/32/16) via ImageMagick. Uncomment
win.icon in electron-builder.yml so installers stop falling back to the default
Electron icon. Marks CODE-AUDIT.md M3 placeholder-done; a designed asset is
still wanted before v1.0.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
