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/public/content/about-us.md

@@ -0,0 +1,26 @@
+# About Us
+
+## Lorem Ipsum
+
+Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.
+
+## Dolor Sit Amet
+
+Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat:
+
+- **Duis aute irure** - Dolor in reprehenderit in voluptate velit esse cillum dolore
+- **Eu fugiat nulla** - Pariatur excepteur sint occaecat cupidatat non proident
+- **Sunt in culpa** - Qui officia deserunt mollit anim id est laborum
+- **Sed ut perspiciatis** - Unde omnis iste natus error sit voluptatem
+
+## Consectetur Adipiscing
+
+Sed ut perspiciatis unde omnis iste natus error sit voluptatem accusantium doloremque laudantium, totam rem aperiam, eaque ipsa quae ab illo inventore veritatis et quasi architecto beatae vitae dicta sunt explicabo.
+
+## Nemo Enim
+
+Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit, sed quia consequuntur magni dolores eos qui ratione voluptatem sequi nesciunt.
+
+---
+
+*For questions or feedback, [contact us](/contact).*