Build and deployment speed of test apps

The recent rebuild of review to test apps #41 (closed) has lead to a regression in page deployment #58 (closed).

Further analysis of the situation in #62 (closed) has reminded us of the conclusion of the original rebuild story in #41 (comment 42420), namely that there is a nice integration of GitLab pages with GitLab pipeline job artifacts, which makes them available in a browsable state. Given

• The CI pipeline uses an astro build command that accepts an environment variable for the base setting, and builds a preview environment from it

Then the deployment speed of test apps for review reduces to the time to run the test build.