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/label/Label.vue

@@ -0,0 +1,31 @@
+<script setup lang="ts">
+import { type HTMLAttributes, computed } from 'vue'
+import { Label as LabelPrimitive } from 'reka-ui'
+import { cn } from '@/lib/utils'
+
+interface LabelProps {
+  for?: string
+  class?: HTMLAttributes['class']
+}
+
+const props = defineProps<LabelProps>()
+
+const delegatedProps = computed(() => {
+  const { class: _, ...delegated } = props
+  return delegated
+})
+</script>
+
+<template>
+  <LabelPrimitive
+    v-bind="delegatedProps"
+    :class="
+      cn(
+        'text-sm font-medium leading-none peer-disabled:cursor-not-allowed peer-disabled:opacity-70',
+        props.class
+      )
+    "
+  >
+    <slot />
+  </LabelPrimitive>
+</template>