fix: use .all instead of .exists() to respect prefetch cache in plant_detail

plants/templates/plants/plant_detail.html

@@ -77,7 +77,7 @@
     {% include "plants/partials/photo_gallery.html" %}
 </div>
 
-{% if plant.card_photos.exists %}
+{% if plant.card_photos.all %}
 <a href="{% url 'plant_card' plant.pk %}" class="btn btn-sm btn-outline-secondary mb-2">🪧 View plant card</a>
 {% endif %}