Pure member movement into MainViewModel.License.cs (zero behavior change):
Polar license state (LicenseKey/LicenseMessage/IsLicenseValidating/
IsLicenseEntryOpen/IsHubVisible/IsPremium + OfflineGracePeriod),
ValidateLicenseAtStartupAsync, ActivateLicenseAsync. docs in same commit:
ViewModels/index.md split table (License ✔).
