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/NavMenu.razor

@@ -4,15 +4,29 @@
 
 @code {
     [Parameter] public bool IsCollapsed { get; set; }
+    [Parameter] public EventCallback OnToggleSidebar { get; set; }
+
+    private Task ToggleSidebarAsync()
+    {
+        return OnToggleSidebar.InvokeAsync();
+    }
 }
 
 <div class="nav-menu-shell @(IsCollapsed ? "nav-menu-shell-collapsed" : string.Empty)" data-testid="sidebar-shell" data-collapsed="@(IsCollapsed ? "true" : "false")">
-<div class="top-row ps-3 navbar navbar-dark">
-    <div class="container-fluid">
-        <a class="navbar-brand" href="" aria-label="WorkTracker home">
-            <span class="sidebar-brand-full">WorkTracker</span>
-            <span class="sidebar-brand-compact" aria-hidden="true">WT</span>
-        </a>
+<div class="top-row ps-3 pe-3 navbar navbar-dark">
+    <div class="container-fluid nav-menu-header">
+        <button
+            type="button"
+            class="sidebar-toggle"
+            @onclick="ToggleSidebarAsync"
+            aria-label="Toggle sidebar"
+            aria-controls="sidebar-navigation"
+            aria-expanded="@(IsCollapsed ? "false" : "true")"
+            title="Toggle sidebar">
+            <span class="sidebar-toggle-bar"></span>
+            <span class="sidebar-toggle-bar"></span>
+            <span class="sidebar-toggle-bar"></span>
+        </button>
     </div>
 </div>