refactor: migrate to DDD layered architecture
Split the monolithic app.rs (762 lines) into four DDD layers:
- domain/: models, navigation enums (Tab, ModalKind), conversions, aggregates
- application/: App state, LibraryState, NotificationManager, event handlers
- infrastructure/: config, gRPC client, system utilities
- presentation/: all render functions, widgets, views, modals
Original modules (app, data, ui, config, grpc) preserved as thin
re-export facades for backward compatibility. All 13 insta snapshot
tests pass without modification.
Alexander
c1205e5fb0