Add unit tests for core components and layouts

- **ThemeToggle:** Introduce comprehensive tests to validate button functionality, dropdown options, and active theme indicators.
- **ThemeProvider:** Add tests for theme management, localStorage persistence, system preferences, and DOM updates.
- **Header & Footer:** Verify header rendering, user menu functionality, and footer content consistency.
- **AuthInitializer:** Ensure authentication state is correctly loaded from storage on mount.

frontend/tests/components/layout/Footer.test.tsx

@@ -0,0 +1,33 @@
+/**
+ * Tests for Footer Component
+ * Verifies footer rendering and content
+ */
+
+import { render, screen } from '@testing-library/react';
+import { Footer } from '@/components/layout/Footer';
+
+describe('Footer', () => {
+  describe('Rendering', () => {
+    it('renders footer element', () => {
+      const { container } = render(<Footer />);
+
+      const footer = container.querySelector('footer');
+      expect(footer).toBeInTheDocument();
+    });
+
+    it('displays copyright text with current year', () => {
+      render(<Footer />);
+
+      const currentYear = new Date().getFullYear();
+      expect(screen.getByText(`© ${currentYear} FastNext Template. All rights reserved.`)).toBeInTheDocument();
+    });
+
+    it('applies correct styling classes', () => {
+      const { container } = render(<Footer />);
+
+      const footer = container.querySelector('footer');
+      expect(footer).toHaveClass('border-t');
+      expect(footer).toHaveClass('bg-muted/30');
+    });
+  });
+});