test(meds): green the wizard e2e locale and one-shot timezone fixtures

The medication-wizard e2e specs assert the German step counter, but the
seeded e2e user falls back to the English default locale; pin the
`healthlog-locale=de` cookie for the wizard flow and correct the
storage-state cookie allowlist to the hyphenated cookie name the i18n
layer actually reads.

The one-shot cadence integration fixture derived `startsOn`/`endsOn` from
the UTC calendar date but checked emission against the Europe/Berlin
today-window, so the assertion flipped when the suite ran in the UTC
evening. Derive the fixture dates from the same Berlin calendar day the
window uses.

Also refresh the OpenAPI spec version to 1.6.0.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/api/openapi.yaml

@@ -1,7 +1,7 @@
 openapi: 3.1.0
 info:
   title: HealthLog API
-  version: 1.5.6
+  version: 1.6.0
   description: >-
     Self-hosted personal-health-tracking PWA — public API surface for the iOS native client and external ingest.