Android Drop

Add brand app/menu-bar/Dock icons and polish the Mac settings window

- icons.py: draw the menu-bar (template arrows), Dock and Finder icons from code
  using the SF Symbol arrow.up.arrow.down, matching the Android logo. make_icon.py
  generates AppIcon.icns at build time (gitignored); build_app.sh runs it.
- Menu-bar item now shows the arrows icon instead of the "⬇" text.
- Set the Dock icon when the settings window opens (setApplicationIconImage_), so it
  shows our icon even when run via `python app.py` instead of Python's rocket.
- Redesigned settings window: logo header + title/subtitle, colored status dot
  (green when a phone is connected), section labels, separators, accent Save button.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>