feat(site): root opens the main gym; other gyms as navbar buttons

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

site/includes/navbar.php

@@ -47,6 +47,22 @@ $logo_dims = svg_img_dims_attr(dirname(__DIR__, 2) . '/' . $logo_rel);
         </li>
         <?php endforeach; ?>
       </ul>
+      <?php
+      // Other published gyms: the main gym opens first, the rest are
+      // highlighted buttons at the right end of the bar.
+      $other_gyms = [];
+      if (!empty($GLOBALS['pdo'])) {
+          foreach (db_gyms_published($GLOBALS['pdo']) as $g) {
+              if ((int) $g['id'] !== (int) current_gym()['id']) $other_gyms[] = $g;
+          }
+      }
+      if ($other_gyms): ?>
+      <div class="gym-switch d-flex flex-wrap gap-2 ms-lg-auto py-2 py-lg-0 pe-lg-3">
+        <?php foreach ($other_gyms as $g): ?>
+        <a class="gym-switch-btn" href="<?= htmlspecialchars(gym_url($g)) ?>"><?= htmlspecialchars($g['name']) ?></a>
+        <?php endforeach; ?>
+      </div>
+      <?php endif; ?>
     </div>
   </nav>
 </header>