fix: optimize catalog mobile cart behavior and z-index hierarchy

- Fix cart overlay blocking header in mobile (z-index: header 900 < cart 1000)
- Add cart-is-collapsed class with translateY(calc(100% - 60px)) for bottom sheet behavior
- Ensure cart header remains visible and clickable when collapsed in mobile
- Add deep Vuetify styles for search field integration (:deep(.v-field))
- Preserve desktop sticky sidebar behavior (position: sticky, overflow-y: auto)
- Make entire cart header clickable in mobile (@click on v-card-title)
- Add visual feedback with chevron icons (mdi-chevron-up/down)
- Clean CSS organization with section comments

src/components/catalog/Cart.vue

@@ -7,7 +7,7 @@
     <v-card-title 
       class="d-flex align-center cart-title"
       :class="{ 'cart-header-mobile': isMobile, 'cart-header-desktop': !isMobile }"
-    >
+      @click="isMobile && $emit('toggle-collapse')">
       <!-- Icono del carrito - SIEMPRE VISIBLE -->
       <v-icon class="mr-2">mdi-cart</v-icon>