Prune and fix CI test suites

Review all test suites, delete stale, superseeded, those that were one off to check feature flags or absence of something. Kill the most long running or flaky with unit tests that execute in milliseconds. Regroup between quick and full, Fix broken tests in CI - GitHub Actions - look at a few recent test runs and fix broken/flaky tests. Babysit CI/CD until the tests (test.yaml) pass.

Fixed test.yml red: main's IAM boundary back under the 6,144 cap (6,289→6,115, nothing widened) and a flaky split-width smoke assertion. Full gate green 746s; PR #5757 merged, deploy succeeded. Sweeps found nothing to prune. test.yml itself unverified until the next promotion PR (human-gated, none open).