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/SelectContent.vue

@@ -0,0 +1,43 @@
+<script setup lang="ts">
+import { type HTMLAttributes, computed } from 'vue'
+import { SelectContent as SelectContentPrimitive, SelectPortal, SelectViewport } from 'reka-ui'
+import { cn } from '@/lib/utils'
+
+interface SelectContentProps {
+  position?: 'popper' | 'item-aligned'
+  class?: HTMLAttributes['class']
+}
+
+const props = withDefaults(defineProps<SelectContentProps>(), {
+  position: 'popper',
+})
+
+const delegatedProps = computed(() => {
+  const { class: _, ...delegated } = props
+  return delegated
+})
+</script>
+
+<template>
+  <SelectPortal>
+    <SelectContentPrimitive
+      v-bind="delegatedProps"
+      :class="
+        cn(
+          'relative z-50 min-w-[8rem] overflow-hidden rounded-md border bg-popover text-popover-foreground shadow-md data-[state=open]:animate-in data-[state=closed]:animate-out data-[state=closed]:fade-out-0 data-[state=open]:fade-in-0 data-[state=closed]:zoom-out-95 data-[state=open]:zoom-in-95 data-[side=bottom]:slide-in-from-top-2 data-[side=left]:slide-in-from-right-2 data-[side=right]:slide-in-from-left-2 data-[side=top]:slide-in-from-bottom-2',
+          props.position === 'popper' &&
+            'data-[side=bottom]:translate-y-1 data-[side=left]:-translate-x-1 data-[side=right]:translate-x-1 data-[side=top]:-translate-y-1',
+          props.class
+        )
+      "
+    >
+      <SelectViewport
+        :class="
+          cn('p-1', props.position === 'popper' && 'h-[var(--reka-select-trigger-height)] w-full min-w-[var(--reka-select-trigger-width)]')
+        "
+      >
+        <slot />
+      </SelectViewport>
+    </SelectContentPrimitive>
+  </SelectPortal>
+</template>