* feat(#14): migrate App.xaml + App.xaml.cs to Avalonia bootstrap
- App.xaml: replace WPF/AdonisUI xmlns with Avalonia xmlns=https://github.com/avaloniaui; add FluentTheme; remove AdonisUI MergedDictionaries and BooleanToVisibilityConverter (Views/Resources/* will be re-added as they are migrated in later issues)
- App.xaml.cs: inherit Avalonia.Application; OnFrameworkInitializationCompleted replaces OnStartup; AppExit wired via IClassicDesktopStyleApplicationLifetime.Exit; AdonisUI MessageBox replaced with inline Avalonia Window dialog; P/Invokes guarded with OperatingSystem.IsWindows(); GetRegistryValue guarded for Linux (P3-006 will replace fully)
- Program.cs (new): Avalonia entry point with BuildAvaloniaApp + Main; AppDomain.UnhandledException registered to drive ShowErrorDialog
- AssemblyInfo.cs: remove WPF ThemeInfoAttribute (no Avalonia equivalent)
- FModel.csproj: StartupObject -> FModel.Program; add Serilog.Sinks.Console 6.1.1 (needed for AnsiConsoleTheme in debug logger); exclude Properties/Resources.resx + Designer.cs (WPF boilerplate, unreferenced)
Closes#14
* fix(#14): address code review findings in App bootstrap
[C1] Replace AppDomain.UnhandledException with Dispatcher.UIThread
.UnhandledExceptionFilter — fires on UI thread, allows Handled=true
[C2] Wrap dialog.Show() fallback in try/catch; return early if app is
shutting down to avoid silent crash
[M1] Add TODO(#15) comment for desktop.MainWindow assignment
[M2] Change Dispatcher.UIThread.Post → InvokeAsync; restructure
ShowErrorDialog to only use tcs.Task in the modeless path
[M3] Restore Environment.Exit(0) in AppExit to preserve original
termination behaviour until proper cancellation is in place
[m2] Add SolidColorBrush resources (AccentColorBrush, AlertColorBrush,
ErrorColorBrush) alongside Color resources in App.xaml
* fix(#14): address second-pass review findings
[m1/s1] Move Dispatcher.UIThread.UnhandledExceptionFilter subscription
to after Log.Logger is configured; Log.Error calls inside the
handler were no-ops when exceptions occurred during the ~80-line
init block (settings load, directory creation)
[m2] Attach .ContinueWith(OnlyOnFaulted) to the InvokeAsync task in
ShowErrorDialog so secondary exceptions in the error-handling
path (UserSettings.Delete, Restart) are logged rather than
silently swallowed as unobserved task faults
* Address review feedback
