Bugfix: bind MoleculeViewModels as ViewModel and complete Metro wiring

[panasetskaya]

After the Koin→Metro migration, the app crashed on startup:

  java.lang.IllegalArgumentException: Unknown model class CrossSellSheetViewModel                                                                                      
      at dev.zacsweers.metrox.viewmodel.MetroViewModelFactory.create(...)      

Root cause

Metro's @ContributesIntoMap infers the bound type from a class's single declared supertype. Our ViewModels extend MoleculeViewModel<Event, State>, so they were contributed as MoleculeViewModel<…> instead of ViewModel — and never landed in the Map<KClass<out ViewModel>, () -> ViewModel> that MetroViewModelFactory reads. They were silently dropped, then crashed when first requested. 40 ViewModels were affected (assisted-factory ViewModels were not, since they bind via a factory interface).

Fixing that surfaced a second layer: because the dropped ViewModels were never validated, the graph compiled despite genuinely missing dependency bindings. Once the VMs were correctly in the graph, Metro reported 10 MissingBinding errors.

Decisions

• binding<ViewModel>() — per Metro's docs, a ViewModel that extends an intermediate base must specify the bound type explicitly. Applied to all 40 MoleculeViewModel subclasses.
• Public provider surface over graph extensions — feature-internal Provider<UseCase> bindings couldn't feed the single shared AppGraph (:app can only reference public types). Graph extensions were considered but rejected: a parent graph can't see child-extension bindings, and MetroViewModelFactory lives in the parent — so they'd require re-architecting how every screen resolves its ViewModel. Instead we made the relevant use cases/repositories + their providers public, matching the existing pattern (cross-sell already worked because its model lives in a public module).
• ApplicationScope over raw CoroutineScope — HomeViewModel was the lone outlier injecting CoroutineScope; switched to ApplicationScope like the rest of the codebase.
• Assisted factories for SavedStateHandle — SavedStateHandle is only available via CreationExtras at creation time, not as a graph binding, so those ViewModels were converted to metrox's ViewModelAssistedFactory.

Changes

• 40 ViewModels: added binding<ViewModel>() to @ContributesIntoMap.
• data-addons: provide Provider<GetAddonBannerInfoUseCase> (base type) from DataAddonsMetroProviders.
• cross-sell, forever, home, payments, profile: made use-case/repository interfaces, impls, demos, providers and @ContributesTo modules public so their Provider bindings reach AppGraph (includes the public model cascade, e.g. HomeData, PaymentOverview, ContactInformation).
• home: bound SeenImportantMessagesStorage (@Inject + @ContributesBinding); HomeViewModel/HomePresenter now inject ApplicationScope.
• SavedStateHandle VMs (SwedishLogin, movingflow EnterNewAddress / AddHouseInformation / Summary): converted to @AssistedInject + nested ViewModelAssistedFactory; call sites updated to assistedMetroViewModel().