Clean 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.

Merged #5620. CI test.yml has no open failures after a 51-job audit. The bundle selftests are 5x and 1.5x faster (the bundle one sat on CI's first-wave critical path). Deleted 3 stale migration tests and fixed 2 assertions that could never fail. The deploy succeeded. Moving quick-tier stages to full was rejected after measuring it (~2s saved per commit). Deferred: a timing gap in the platform reproducibility test.