feat(content): add About Us page with markdown content support

- Create AboutUsPage component with markdown rendering
- Add react-markdown library for content rendering
- Create public/content directory for editable markdown files
- Add about-us.md with Lorem Ipsum placeholder content
- Create public/images/about directory for page images
- Add /about-us route in App.jsx
- Add About Us link to homepage footer
- Support for external links (open in new tab) and internal links
- Responsive image rendering with rounded corners and shadow

frontend/src/pages/HomePage.jsx

@@ -274,6 +274,11 @@ const HomePage = () => {
             <div>
               <h3 className="text-white font-semibold mb-4">Support</h3>
               <ul className="space-y-2 text-sm">
+                <li>
+                  <Link to="/about-us" className="hover:text-primary-400 transition">
+                    About Us
+                  </Link>
+                </li>
                 <li>
                   <Link to="/contact" className="hover:text-primary-400 transition">
                     Contact Us