Test suite cleanup and CI pipeline stabilization

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 #6712 (ebca67b), dev deploy green: fixed the cron-ledger CI flake (forced repro), fixed an e2e test broken by Task 9214, retired 4 applied one-shot migration tests. Quick/full regroup rejected with measurements; test.yml next runs on a promotion PR. Memory: proposed 1 gotcha.