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/Views/MainWindow.xaml

@@ -175,7 +175,11 @@
                                VerticalAlignment="Center" Margin="0,0,8,0" />
                     <Button Style="{StaticResource SecondaryButton}"
                             Content="🔑  Activer / changer"
-                            Command="{Binding ActivateLicenseCommand}" />
+                            Command="{Binding ActivateLicenseCommand}"
+                            Margin="0,0,8,0" />
+                    <Button Style="{StaticResource SecondaryButton}"
+                            Content="⚙  Paramètres"
+                            Command="{Binding OpenSettingsCommand}" />
                 </StackPanel>
             </Grid>
         </Border>