Improve system tray icons and CLI table formatting

System tray improvements:
- Replace SVG rendering with pre-rendered 64x64 transparent PNG icons
  for better compatibility across desktop environments
- Add four icon variants: idle, syncing, error, suspended
- Include source artwork files (autogit.svg, autogit.png)
- Remove unused code: start_time field, toggle_suspend, reset_errors,
  format_uptime, format_time_ago methods
- Add comprehensive test suite for tray.rs (22 tests covering all
  states, icon loading, menu behavior, and suspend/resume logic)

CLI improvements:
- Fix status column width in list command to be compact (11 chars)
- Allow Path and Commit Message columns to grow naturally up to 60 chars
- Improve table readability with better proportions

Author: awalland