Add comprehensive tests for services (ConnectionTestService, RuntimeConfigValidation),
ViewModels (PipelineEditor, dialogs, transformers), and Avalonia headless UI tests
for views and forms.
Eliminates placeholder substitution (${KEY}) in favor of storing complete
connection strings as single encrypted values. SecureStore now auto-creates
entries for all connection strings defined in appsettings. ConfigManager
editor reads/writes values directly to SecureStore.
Adds a new ConnectionStrings section to ConfigManager allowing users to manage
database connection strings with provider selection, connection testing, and
visual feedback for connection state.
Joseph Doherty