thor-watcher had no icon.ico, so build.bat's 'if exist icon.ico' check
always fell through to building without --icon → PyInstaller's default
Python/floppy icon. Reuse the shared Terra-Mechanics icon from
series3-watcher; build.bat now picks it up automatically (no script
change needed). Rides with the pending 0.4.1 build.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
