Refactor SignalR client DI and config, add test factory
Refactored FruitBankSignalRClient construction to use DI and centralized configuration from appsettings.json across all platforms. Introduced TestSignalRClientFactory for consistent test setup. Added FruitBankHubConnectionExtensions for reusable SignalR connection and logging configuration. Updated Program.cs and MauiProgram.cs to register logger factories, log writers, and IHubConnectionBuilder via DI. Embedded appsettings.json in MAUI and updated .csproj references for build flexibility. No business logic changes; all updates are infrastructure and test setup.
Introduces ISecureCredentialService abstraction and platform-specific implementations for secure credential storage (WebAssembly, MAUI, server). Refactors LoggedInModel to support async auto-login, login, and logout using stored credentials. Updates DI and UI logic to enable seamless auto-login and logout across all platforms. Cleans up redundant navigation checks and improves maintainability.