MainViewModel.Overlays.cs (194 lines) takes the settings/bug/feature/about
panels + creator-hub links: panel state (IsSettingsOpen/IsBugOpen/IsFeatureOpen/
IsAboutOpen via SetPanel, IsLicensesOpen, IsAnyOverlayOpen, OverlayTitle),
ShowOverlay/ShowLicenses, bug/feature report fields + SubmitBug/SubmitFeature/
ComposeEmail/OpenUrl, the About-hub consts (ChannelUrl/MastodonUrl/CoffeeUrl/
PremiumUrl/IsPremiumAvailable), SupportEmail/AppVersionLabel, LicensesText, and
the overlay command declarations (OpenSettingsCommand..OpenLicensesCommand).
Core drops 940 -> 758 lines. Ctor command assignments and all other wiring stay
in core; SetPanel/ShowOverlay keep their cross-partial calls.
This completes Phase 1: MainViewModel.cs has been split into 10 functional
partials (1,890 -> 758 lines in core).
Zero behavior change; build 0 warnings; 246 pass, only the 2 known failures.
Docs: index.md Overlays row added, About-hub row re-pointed, tracker marked
Phase 1 complete in the same commit.
