feat(pos): Display showcase kits in POS interface

- Added get_showcase_kits_for_pos() function to retrieve showcase kits with active reservations
- Modified POS terminal to show showcase kits when 'Витрина' button is clicked
- Showcase kits displayed as product cards with showcase name badge (🌺 icon)
- Added isShowcaseView flag to toggle between regular and showcase view modes
- Implemented distinct styling for active showcase button:
  * Bright orange background (#ff6600)
  * Black text for contrast
  * Thicker border (3px)
  * Enhanced shadow and scale effect (1.05)
- Showcase kits can be added to cart for sale from POS interface

myproject/pos/templates/pos/terminal.html

@@ -159,6 +159,7 @@
 <!-- Hidden data containers for JavaScript -->
 <script id="categoriesData" type="application/json">{{ categories_json|safe }}</script>
 <script id="itemsData" type="application/json">{{ items_json|safe }}</script>
+<script id="showcaseKitsData" type="application/json">{{ showcase_kits_json|safe }}</script>
 
 <script src="{% static 'pos/js/terminal.js' %}"></script>
 {% endblock %}