feat(orders): pass the CMS's status and safe error fields to the browser

The order routes (get, put, add-product, remove-product, checkout, capture)
call forwardToCms, which throws a CMS error on as
createError({ statusCode, statusMessage, data: { message, errors?, missing? } }),
built by the pure shopErrorFromCms (server/utils/cmsError.ts).

Before, the FetchError was thrown on as it was: the browser got the CMS's
status, but Nitro treated it as unhandled, answered "Server Error" without
data and logged every CMS 4xx as [unhandled]. Now the browser also gets the
CMS's message, the errors of a rejected update and the fields a checkout
misses, and no other field. A status that is the shop's own fault (401, 403,
...) is answered 500, a CMS that does not answer 503; 5xx are logged without
the query and the order uuid.

npm test runs tests/unit with Node's type stripping and no dependencies, as
in libreshop/cms. nuxt.config keeps tests/ out of the app's type check.

Refs libretech/mp#71

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",