Right sidebar nav: Library / Reports / Documentation tabs (WebView2)

The body of the launcher is now a 2-column layout:
- Left : swappable content area
- Right (200px) : sidebar with 3 nav buttons + active-state highlighting

Three pages, all under the same window chrome / footer:

1. **Library** (default) — the existing main view (featured version,
   other versions list, floating "Vérifier les MAJ" button, copyright).
2. **Reports** — embedded WebView2 navigated to a configurable URL.
   Default http://localhost/ProserveReport/ which matches the local
   stats tool installed on each customer machine alongside XAMPP.
3. **Documentation** — WebView2 with a configurable URL, falls back
   to a placeholder explaining where to set it if empty.

Implementation
- LocalConfig gains ReportUrl + DocumentationUrl (string).
- MainViewModel gains LauncherPage enum + CurrentPage state with
  Navigate{Library,Report,Documentation}Command. ReportUri /
  DocumentationUri parse the strings to Uri for WebView2.Source.
- Theme.xaml: NavButton style (transparent, left-aligned, hover
  darken, active state highlighted via Tag bool + accent left-border).
- InverseBoolToVisibilityConverter added (true → Collapsed) for the
  documentation placeholder fallback.
- Microsoft.Web.WebView2 NuGet (1.0.2792.45). Runtime is pre-installed
  on Win11 and auto-pushed via Windows Update on Win10. If absent,
  WebView2 surfaces an error which the user sees inline.
- Settings → Avancés → Serveur extended with the two URL fields.
- Strings.cs: NavLibrary / NavReport / NavDocumentation,
  SettingsReportUrl / SettingsDocsUrl, DocsPlaceholder, WebViewLoadError.
  Sidebar localized in 5 languages.

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

src/PSLauncher.App/ViewModels/MainViewModel.cs

@@ -21,6 +21,12 @@ using PSLauncher.Models;
 
 namespace PSLauncher.App.ViewModels;
 
+/// <summary>
+/// Onglets affichés dans la sidebar droite du launcher. Chacun correspond à un
+/// bloc de contenu visible/caché dans la fenêtre principale.
+/// </summary>
+public enum LauncherPage { Library, Report, Documentation }
+
 public sealed partial class MainViewModel : ObservableObject
 {
     private readonly IInstallationRegistry _registry;
@@ -68,6 +74,34 @@ public sealed partial class MainViewModel : ObservableObject
 
     [ObservableProperty] private double _progressPercent;
 
+    /// <summary>
+    /// Onglet actuellement actif dans la sidebar droite. La UI montre le bon bloc
+    /// via les converters IsLibrary / IsReport / IsDocumentation. Default = Library
+    /// pour que le launcher s'ouvre directement sur l'écran principal.
+    /// </summary>
+    [ObservableProperty]
+    [NotifyPropertyChangedFor(nameof(IsLibrary))]
+    [NotifyPropertyChangedFor(nameof(IsReport))]
+    [NotifyPropertyChangedFor(nameof(IsDocumentation))]
+    private LauncherPage _currentPage = LauncherPage.Library;
+
+    public bool IsLibrary       => CurrentPage == LauncherPage.Library;
+    public bool IsReport        => CurrentPage == LauncherPage.Report;
+    public bool IsDocumentation => CurrentPage == LauncherPage.Documentation;
+
+    /// <summary>URL résolue pour le panneau Reports. WebView2.Source attend un Uri.</summary>
+    public Uri? ReportUri => TryParseUri(_config.ReportUrl);
+    /// <summary>URL résolue pour le panneau Documentation. Null si non configurée.</summary>
+    public Uri? DocumentationUri => TryParseUri(_config.DocumentationUrl);
+    public bool HasDocumentationUrl => DocumentationUri is not null;
+
+    private static Uri? TryParseUri(string? s)
+        => !string.IsNullOrWhiteSpace(s) && Uri.TryCreate(s, UriKind.Absolute, out var u) ? u : null;
+
+    [RelayCommand] private void NavigateLibrary()       => CurrentPage = LauncherPage.Library;
+    [RelayCommand] private void NavigateReport()        => CurrentPage = LauncherPage.Report;
+    [RelayCommand] private void NavigateDocumentation() => CurrentPage = LauncherPage.Documentation;
+
     [ObservableProperty]
     [NotifyPropertyChangedFor(nameof(FooterText))]
     [NotifyPropertyChangedFor(nameof(FooterVisibility))]