Implement shopping cart functionality with UI components and API integration

- Added CartItem, CartSummary, CartEmpty, CartSidebar, and CartSheet components for managing cart display and interactions.
- Integrated useCart and useCartUI composables for cart state management and UI control.
- Implemented API endpoints for cart operations, including fetching, adding, updating, and removing items.
- Enhanced user experience with loading states and notifications using vue-sonner for cart actions.
- Configured session management for guest and authenticated users, ensuring cart persistence across sessions.

This commit completes the shopping cart feature, enabling users to add items, view their cart, and proceed to checkout.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

app/components/ui/sonner/Sonner.vue

@@ -0,0 +1,23 @@
+<script lang="ts" setup>
+import type { ToasterProps } from "vue-sonner"
+import { Toaster as Sonner } from "vue-sonner"
+
+const props = defineProps<ToasterProps>()
+</script>
+
+<template>
+  <Sonner
+    class="toaster group"
+    v-bind="props"
+    :toast-options="{
+      classes: {
+        toast: 'group toast group-[.toaster]:bg-background group-[.toaster]:text-foreground group-[.toaster]:border-border group-[.toaster]:shadow-lg',
+        description: 'group-[.toast]:text-muted-foreground',
+        actionButton:
+          'group-[.toast]:bg-primary group-[.toast]:text-primary-foreground',
+        cancelButton:
+          'group-[.toast]:bg-muted group-[.toast]:text-muted-foreground',
+      },
+    }"
+  />
+</template>