Enhance checkout flow with new components and validation

- Added AddressForm and CheckoutForm components for user input during checkout.
- Implemented validation using Zod and VeeValidate for billing address fields.
- Created OrderSummary and MockPayPalButton components for order confirmation and payment simulation.
- Updated CartSheet and CartSidebar to navigate to the new checkout page at '/kasse'.
- Introduced new API endpoints for validating checkout data and creating orders.
- Enhanced user experience with responsive design and error handling.

These changes complete the checkout functionality, allowing users to enter billing information, simulate payment, and confirm orders.

app/components/ui/select/SelectTrigger.vue

@@ -0,0 +1,33 @@
+<script setup lang="ts">
+import { type HTMLAttributes, computed } from 'vue'
+import { SelectTrigger as SelectTriggerPrimitive } from 'reka-ui'
+import { ChevronDown } from 'lucide-vue-next'
+import { cn } from '@/lib/utils'
+
+interface SelectTriggerProps {
+  disabled?: boolean
+  class?: HTMLAttributes['class']
+}
+
+const props = defineProps<SelectTriggerProps>()
+
+const delegatedProps = computed(() => {
+  const { class: _, ...delegated } = props
+  return delegated
+})
+</script>
+
+<template>
+  <SelectTriggerPrimitive
+    v-bind="delegatedProps"
+    :class="
+      cn(
+        'flex h-10 w-full items-center justify-between rounded-md border border-input bg-background px-3 py-2 text-sm ring-offset-background placeholder:text-muted-foreground focus:outline-none focus:ring-2 focus:ring-ring focus:ring-offset-2 disabled:cursor-not-allowed disabled:opacity-50',
+        props.class
+      )
+    "
+  >
+    <slot />
+    <ChevronDown class="h-4 w-4 opacity-50" />
+  </SelectTriggerPrimitive>
+</template>