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/App.jsx

@@ -21,6 +21,7 @@ import PublicProfilePage from './pages/PublicProfilePage';
 import ActivityLogsPage from './pages/admin/ActivityLogsPage';
 import ContactMessagesPage from './pages/admin/ContactMessagesPage';
 import ContactPage from './pages/ContactPage';
+import AboutUsPage from './pages/AboutUsPage';
 import NotFoundPage from './pages/NotFoundPage';
 import VerificationBanner from './components/common/VerificationBanner';
 import InstallPWA from './components/pwa/InstallPWA';
@@ -228,6 +229,9 @@ function App() {
           {/* Contact Page - Public route */}
           <Route path="/contact" element={<ContactPage />} />
 
+          {/* About Us Page - Public route */}
+          <Route path="/about-us" element={<AboutUsPage />} />
+
           {/* Public Profile - /u/username format (no auth required) */}
           <Route path="/u/:username" element={<PublicProfilePage />} />