v0.5: settings dialog, persistent Serilog logs, Windows toasts

Settings (⚙ button in top bar)
------------------------------
SettingsDialog opens via OpenSettings command in MainViewModel. Sections:
- Serveur: server URL field + "Tester" button that GETs /api/health
  and reports status inline.
- Installation: installRoot path with Browse button
  (Microsoft.Win32.OpenFolderDialog, .NET 8 native).
- License: shows status / owner / exp / machine ID (read-only,
  copy-to-clipboard button), "Désactiver" wipes the cached license.
- Cache: shows download cache path + current size, opens or empties it.
- Logs & Application: launcher version + logs path with "Open" button.

Apply persists to LocalConfig via IConfigStore. After save, MainViewModel
RebuildList()s so changes to ServerBaseUrl or InstallRoot take effect
without restart.

Persistent Serilog logs
-----------------------
Logs now live in %LocalAppData%/PSLauncher/logs/app-YYYYMMDD.log, rolling
daily, 10 days kept. Output template includes source context and stack
traces. Generic Host wired up via .UseSerilog() so all
ILogger<T>-injected types share the sink. Unhandled AppDomain and
Dispatcher exceptions are routed to Serilog before propagation.

Windows toasts
--------------
IToastService + ToastService backed by Microsoft.Toolkit.Uwp.Notifications
(ToastContentBuilder.Show()). Required bumping the App TFM from
net8.0-windows to net8.0-windows10.0.17763.0 (with explicit
WindowsSdkPackageVersion=10.0.17763.41 to satisfy CommunityToolkit.Mvvm
8.3.2's MVVMTKCFG0003 check). Triggered on:
- successful install completion: "Proserve v{X} est prête à être lancée"
- install/download error: short error excerpt

Misc
----
- InverseBoolConverter for "disable button while busy" patterns.
- Added Markdig.Wpf import to ReleaseNotesViewerDialog (was implicit
  before, now required explicitly).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/PSLauncher.App/App.xaml.cs

@@ -1,9 +1,11 @@
+using System.IO;
 using System.Net.Http;
 using System.Net.Http.Headers;
 using System.Windows;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
 using Microsoft.Extensions.Logging;
+using PSLauncher.App.Services;
 using PSLauncher.App.ViewModels;
 using PSLauncher.App.Views;
 using PSLauncher.Core.Configuration;
@@ -15,6 +17,7 @@ using PSLauncher.Core.Manifests;
 using PSLauncher.Core.Process;
 using PSLauncher.Core.Updates;
 using PSLauncher.Models;
+using Serilog;
 
 namespace PSLauncher.App;
 
@@ -22,18 +25,46 @@ public partial class App : Application
 {
     private IHost? _host;
 
+    public static string LogsDirectory { get; private set; } = string.Empty;
+
     protected override void OnStartup(StartupEventArgs e)
     {
         base.OnStartup(e);
 
+        // Logs avant tout — pour ne rien perdre des erreurs au boot
+        LogsDirectory = Path.Combine(
+            Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData),
+            "PSLauncher", "logs");
+        Directory.CreateDirectory(LogsDirectory);
+
+        Log.Logger = new LoggerConfiguration()
+            .MinimumLevel.Debug()
+            .Enrich.FromLogContext()
+            .WriteTo.Debug()
+            .WriteTo.File(
+                path: Path.Combine(LogsDirectory, "app-.log"),
+                rollingInterval: RollingInterval.Day,
+                retainedFileCountLimit: 10,
+                outputTemplate: "{Timestamp:yyyy-MM-dd HH:mm:ss.fff} [{Level:u3}] {SourceContext} {Message:lj}{NewLine}{Exception}")
+            .CreateLogger();
+
+        Log.Information("PSLauncher starting (logs in {Path})", LogsDirectory);
+
+        AppDomain.CurrentDomain.UnhandledException += (_, args) =>
+            Log.Fatal((Exception)args.ExceptionObject, "Unhandled exception (AppDomain)");
+        DispatcherUnhandledException += (_, args) =>
+        {
+            Log.Error(args.Exception, "Unhandled UI exception");
+            args.Handled = false;
+        };
+
         _host = Host.CreateDefaultBuilder()
-            .ConfigureLogging(b => { b.ClearProviders(); b.AddDebug(); })
+            .UseSerilog()
             .ConfigureServices((_, services) =>
             {
                 services.AddSingleton<IConfigStore, ConfigStore>();
                 services.AddSingleton<LocalConfig>(sp => sp.GetRequiredService<IConfigStore>().Load());
 
-                // HttpClient partagé (timeout long pour les gros téléchargements)
                 services.AddSingleton(sp =>
                 {
                     var http = new HttpClient(new SocketsHttpHandler
@@ -44,7 +75,7 @@ public partial class App : Application
                     {
                         Timeout = Timeout.InfiniteTimeSpan
                     };
-                    http.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue("PSLauncher", "0.2"));
+                    http.DefaultRequestHeaders.UserAgent.Add(new ProductInfoHeaderValue("PSLauncher", "0.5"));
                     return http;
                 });
 
@@ -75,6 +106,9 @@ public partial class App : Application
                         sp.GetRequiredService<LocalConfig>(),
                         sp.GetRequiredService<ILogger<LicenseService>>()));
 
+                services.AddSingleton<IToastService, ToastService>();
+
+                services.AddTransient<SettingsViewModel>();
                 services.AddSingleton<MainViewModel>();
                 services.AddSingleton<MainWindow>();
             })
@@ -88,6 +122,8 @@ public partial class App : Application
 
     protected override void OnExit(ExitEventArgs e)
     {
+        Log.Information("PSLauncher shutting down");
+        Log.CloseAndFlush();
         _host?.Dispose();
         base.OnExit(e);
     }