Add Colson Duncan's photo with hand-drawn border

Processed colson_duncan.jpg with face detection and border, updated
people.xlsx image reference, rebuilt people.html.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: jeremymanning

data/people.xlsx

@@ -206,7 +206,7 @@ <h3>andy kim | undergrad</h3>
 
             <div class="people-grid">
                 <div class="person-card">
-                    <img src="images/people/placeholder.png" alt="colson duncan">
+                    <img src="images/people/colson_duncan.png" alt="colson duncan">
                     <h3>colson duncan | undergrad</h3>
                     <p>Colson is a '27 studying Neuroscience and Biological Sciences from Los Angeles. He enjoys playing tennis, climbing and playing the guitar.</p>
                 </div>