Extract shared models, services, and application logic into
JdeScoping.ConfigManager.Core library. Add JdeScoping.ConfigManager.Cli
console app with validate, test-connection, and secret commands using
System.CommandLine. UI project now references Core for platform-agnostic
functionality while retaining Avalonia-specific dialog and clipboard services.
Add file system abstraction to enable testability for file operations.
- IFileSystem interface with common file operations
- FileSystem implementation wrapping System.IO
- Unit tests for FileExists functionality