Center last row cards in Community section

- Change community-grid from CSS grid to flexbox
- Add justify-content: center for centering
- Add flex sizing for responsive card layout

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

index.html

@@ -600,9 +600,16 @@
 
         /* Community Section */
         .community-grid {
-            display: grid;
+            display: flex;
-            grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
+            flex-wrap: wrap;
             gap: 2rem;
+            justify-content: center;
+        }
+
+        .community-grid .community-card {
+            flex: 0 1 calc(33.333% - 1.5rem);
+            min-width: 280px;
+            max-width: 380px;
         }
 
         .community-card {