Center last row of 5-card features flexbox

- Switched from grid auto-fit to flexbox with justify-content: center
- Cards: flex-basis 30%, min 260px, max 360px
- Bottom row of 2 cards now centered under 1-2 and 2-3 positions

landing/index.html

@@ -93,13 +93,17 @@
     p { color: var(--text-muted); margin-bottom: 1rem; }
 
     .features {
-      display: grid;
-      grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
+      display: flex;
+      flex-wrap: wrap;
       gap: 1.5rem;
       margin-top: 2rem;
+      justify-content: center;
     }
 
     .feature-card {
+      flex: 1 1 30%;
+      min-width: 260px;
+      max-width: 360px;
       background: var(--bg-card); border: 1px solid var(--border);
       border-radius: 0.75rem; padding: 1.5rem;
       transition: border-color 0.2s ease;