test(embed): run the suite in two more timezones

A transform resolves a report value to dates using local calendar
components, so a test that passes in UTC says nothing about a browser west
of it. test:tz-west and test:tz-east run the whole suite under
America/New_York and Pacific/Auckland; with the UTC construction this test
pair replaces, the bare-number round-trip case fails under the first.

Not wired into CI: it triples the run for a property that is already
pinned by the round-trip assertion, so it stays a local and pre-release
check.

client/package.json

@@ -37,7 +37,9 @@
     "compodoc:build-and-serve": "compodoc -p tsconfig.doc.json -s --name 'Data Controller Client'",
     "compodoc:serve": "compodoc -s --name 'Data Controller Client'",
     "lighthouse": "lhci autorun",
-    "ng": "ng"
+    "ng": "ng",
+    "test:tz-west": "TZ=America/New_York npm run test:headless",
+    "test:tz-east": "TZ=Pacific/Auckland npm run test:headless"
   },
   "private": true,
   "dependencies": {