feat: add theme mode support with AppThemeMode enum and AppThemeState service

- Introduced AppThemeMode enum to define theme options: System, Light, Dark.
- Updated AppSettingsDocument to include ThemeMode property.
- Created AppThemeState service to manage current theme mode and handle changes.
- Integrated theme mode handling in CouchbaseLiteAppSettingsService for persistence.
- Added JavaScript for theme management in the frontend, supporting system preference detection.
- Enhanced CSS with theme variables for consistent styling across light and dark modes.
- Updated Playwright tests to ensure sidebar functionality and responsiveness.

Components/Layout/MainLayout.razor

@@ -1,24 +1,16 @@
 @inherits LayoutComponentBase
+@implements IDisposable
+
+@inject AppThemeState ThemeState
+@inject IJSRuntime JS
 
 <div class="page @(sidebarCollapsed ? "sidebar-collapsed" : string.Empty)">
     <div class="sidebar @(sidebarCollapsed ? "sidebar-collapsed" : string.Empty)">
-        <NavMenu IsCollapsed="sidebarCollapsed" />
+        <NavMenu IsCollapsed="sidebarCollapsed" OnToggleSidebar="ToggleSidebar" />
     </div>
 
     <main>
         <div class="top-row px-4">
-            <button
-                type="button"
-                class="sidebar-toggle"
-                @onclick="ToggleSidebar"
-                aria-label="Toggle sidebar"
-                aria-controls="sidebar-navigation"
-                aria-expanded="@(sidebarCollapsed ? "false" : "true")"
-                title="Toggle sidebar">
-                <span class="sidebar-toggle-bar"></span>
-                <span class="sidebar-toggle-bar"></span>
-                <span class="sidebar-toggle-bar"></span>
-            </button>
             <a href="https://learn.microsoft.com/aspnet/core/" target="_blank">About</a>
         </div>
 
@@ -37,8 +29,39 @@
 @code {
     private bool sidebarCollapsed = true;
 
+    protected override void OnInitialized()
+    {
+        ThemeState.ThemeModeChanged += HandleThemeModeChanged;
+    }
+
+    protected override async Task OnAfterRenderAsync(bool firstRender)
+    {
+        if (!firstRender)
+        {
+            return;
+        }
+
+        var themeMode = await ThemeState.EnsureLoadedAsync();
+        await ApplyThemeAsync(themeMode);
+    }
+
     private void ToggleSidebar()
     {
         sidebarCollapsed = !sidebarCollapsed;
     }
+
+    private void HandleThemeModeChanged(AppThemeMode themeMode)
+    {
+        _ = InvokeAsync(() => ApplyThemeAsync(themeMode).AsTask());
+    }
+
+    private ValueTask ApplyThemeAsync(AppThemeMode themeMode)
+    {
+        return JS.InvokeVoidAsync("workTrackerTheme.setTheme", themeMode.ToString().ToLowerInvariant());
+    }
+
+    public void Dispose()
+    {
+        ThemeState.ThemeModeChanged -= HandleThemeModeChanged;
+    }
 }