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/checkbox/Checkbox.vue

@@ -0,0 +1,41 @@
+<script setup lang="ts">
+import { type HTMLAttributes, computed } from 'vue'
+import { Checkbox as CheckboxPrimitive, CheckboxIndicator } from 'reka-ui'
+import { Check } from 'lucide-vue-next'
+import { cn } from '@/lib/utils'
+
+interface CheckboxProps {
+  checked?: boolean
+  disabled?: boolean
+  class?: HTMLAttributes['class']
+  id?: string
+}
+
+const props = defineProps<CheckboxProps>()
+
+const emit = defineEmits<{
+  'update:checked': [value: boolean]
+}>()
+
+const delegatedProps = computed(() => {
+  const { class: _, ...delegated } = props
+  return delegated
+})
+</script>
+
+<template>
+  <CheckboxPrimitive
+    v-bind="delegatedProps"
+    :class="
+      cn(
+        'peer h-4 w-4 shrink-0 rounded-sm border border-primary ring-offset-background focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-ring focus-visible:ring-offset-2 disabled:cursor-not-allowed disabled:opacity-50 data-[state=checked]:bg-primary data-[state=checked]:text-primary-foreground',
+        props.class
+      )
+    "
+    @update:checked="emit('update:checked', $event)"
+  >
+    <CheckboxIndicator class="flex items-center justify-center text-current">
+      <Check class="h-4 w-4" />
+    </CheckboxIndicator>
+  </CheckboxPrimitive>
+</template>