feat(gyms): gym logo field; other-gym navbar button uses that gym's brand colour and logo

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

site/includes/navbar.php

@@ -59,7 +59,10 @@ $logo_dims = svg_img_dims_attr(dirname(__DIR__, 2) . '/' . $logo_rel);
       if ($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($g['name']) ?></a>
+        <a class="gym-switch-btn" href="<?= htmlspecialchars(gym_url($g)) ?>" style="<?= htmlspecialchars(gym_brand_vars($g)) ?>">
+          <?php if (($g['logo'] ?? '') !== ''): ?><span class="gym-switch-logo" aria-hidden="true" style="--logo:url('<?= htmlspecialchars(base_url($g['logo']), ENT_QUOTES) ?>')"></span><?php endif; ?>
+          <span><?= htmlspecialchars($g['name']) ?></span>
+        </a>
         <?php endforeach; ?>
       </div>
       <?php endif; ?>