Replace mascot with clear device-flow icon

[daredoole]

Summary

• replace the donkey-and-cursor mascot with a clear two-device directional-flow mark
• regenerate Linux application icons, every tray state, Android launcher/themed/notification assets, and raster fallbacks from one SVG source
• add a reproducible icon-generator lockfile and ignore generated work directories

Why

The previous mascot was visually confusing and did not communicate the product’s purpose. The replacement directly represents input moving from one device to another and remains recognizable at 16 px.

Validation

• visually checked at 512 px, 48 px, and pixel-scaled 16 px
• Android debug assemble, unit tests, and lint passed
• generated/source asset consistency checks passed
• repository-wide whitespace and git diff --check passed
• public repository privacy audit passed
• generator dependency audit passed after install with zero vulnerabilities
• updated icon set installed locally; tray restarted successfully without startup or icon errors