This updates the Windows taskbar overlay badge to show ahead and
behind separately with distinct colors, and clears it when both are
zero. It also adds a new authenticated fetch command wired through
the Tauri backend and UI, including a silent background fetch to keep
ahead/behind (and the badge) accurate without user interaction.
- Add Windows dual badge rendering for ahead/behind
- Implement Tauri fetch command with auth error handling
- Add UI fetch action plus periodic background fetch updates
Christoph Brandau
96eb8c109c