feat(site): Add hero imagery and enhance visual design with background images

- Replace gradient backgrounds with high-quality imagery for hero and page sections
- Add 10 new pet care and team member photos (hero, services, team profiles)
- Implement overlay system for hero sections with improved text contrast and readability
- Restructure hero markup with overlay div and hero-content wrapper for proper layering
- Convert about preview section to two-column grid layout with image and content
- Update footer credits to include photo attribution to Unsplash
- Enhance dark mode styling for hero sections with adjusted overlay gradients
- Add responsive grid layout for about section that stacks on mobile devices
- Improve visual hierarchy and brand presentation across all pages

about.html

@@ -160,7 +160,7 @@
             </div>
             <div class="footer-bottom">
                 <p>&copy; 2026 Happy Tails Pet Care. All rights reserved.</p>
-                <p class="footer-credits">Hosted by <a href="https://sloanops.com" target="_blank" rel="noopener">SloanOps</a></p>
+                <p class="footer-credits">Hosted by <a href="https://sloanops.com" target="_blank" rel="noopener">SloanOps</a> · Photos by <a href="https://unsplash.com" target="_blank" rel="noopener">Unsplash</a></p>
             </div>
         </div>
     </footer>