feat: integrate Tailwind CSS and implement dark mode functionality

- Added Tailwind CSS dependencies and configured PostCSS.
- Updated app component to wrap router outlet with a styled div for dark mode support.
- Modified routing to include a default route and added auth guards.
- Implemented dark mode toggle functionality in content component.
- Enhanced login component with improved styling and lifecycle management.
- Created items component with basic structure and routing.
- Added global styles for body and dark mode variants.
- Updated tests for new items component.

Web/src/app/login/login.scss

@@ -0,0 +1,6 @@
+:host {
+    display: flex;
+    flex-direction: column;
+    flex: 1;
+    
+}