feat: Add Credits & Attribution page

- add credits.njk
- add credits.css
- add tooltips.js
- add link in footer

src/_includes/footer.html

@@ -50,7 +50,8 @@
             </li>
         </ul>
     </div>
-    <div id="copyright">&copy; 2025, Derek L. Seitz, <a href="https://dlseitz.dev">dlseitz.dev.</a></div>
+    
+    <div id="copyright">&copy; 2025, Derek L. Seitz, <a href="https://dlseitz.dev">dlseitz.dev</a>. Images used with permissions from <a href="/credits/" target="_blank" rel="noopener noreferrer">these contributors</a>.</div>
 </footer>
 <!-- Custom Newsletter Modal -->
 <div id="custom-alert" class="modal hidden">