Checkout: forward only the checkout fields, show clear errors, fix the contact form (#16)

Co-authored-by: Michael Czechowski <mail@librete.ch>

package.json

@@ -7,7 +7,8 @@
     "dev": "nuxt dev",
     "generate": "nuxt generate",
     "preview": "nuxt preview",
-    "postinstall": "nuxt prepare"
+    "postinstall": "nuxt prepare",
+    "test": "node --experimental-strip-types --import ./tests/unit/support/register.mjs --test 'tests/unit/**/*.test.ts'"
   },
   "dependencies": {
     "@headlessui/vue": "^1.7.23",