ci: nightly ui-tests-matrix — Elasticsearch leg failing (Postgres and MongoDB green)

[angela-helios]

From the 2026-07-30 review call: the nightly UI test matrix (ui-tests-matrix.yml, browser suite against the five storage backends) is succeeding for Postgres and MongoDB but failing on the Elasticsearch leg.

• Pull the failing nightly run's logs/artifacts and identify which specs fail and why (ES-specific search semantics, timing/refresh behavior, or environment).
• Fix the root cause — server-side, test-side, or workflow-side as the evidence dictates.
• A green nightly ES leg, and a note here on what it was.