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/styles.scss

@@ -1 +1,14 @@
 /* You can add global styles to this file, and also import other style files */
+@import "tailwindcss";
+
+@custom-variant dark (&:where(.dark, .dark *));
+
+body {
+    font-family: Arial, sans-serif;
+    min-height: 100vh;
+    min-width: 100vw;
+    margin: 0;
+    box-sizing: border-box;
+    display: flex;
+    flex-direction: column;
+}