Android: Project structure and error handling (pt1)

[keeshux]

Reorganize overall packages (sorted from lowest layer):

• .models = OpenAPI models
• .business = App logic
• .observables = UI logic
• .ui = UI views
• .context = Dependency injection (concrete data)

Error handling:

• Catch risky paths
• Prefer runCatching everywhere
• Rethrow cancellations
• Group custom app exceptions into sealed classes
• Centralize in UI
  • AppCoordinator (see SwiftUI AppCoordinatorConforming)
  • Global error handler
  • Wrap in AppError(Code) before rethrowing
• Wrap JNI library