Now `nupst update` checks current version against latest release before
downloading anything.
Behavior:
- Fetches latest version from Gitea API
- Compares with current version
- Shows "Already up to date!" if versions match
- Only downloads/installs if newer version available
Example output when up to date:
Checking for updates...
Current version: v4.0.8
Latest version: v4.0.8
✓ Already up to date!