Delete stale and flaky 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.

CI test.yml green on develop and branch; no flakes found. Merged #7364 (58bcf14e, deployed): vitest cascade pre-check −9% on slowest files, duplicate api test deleted. Deferred: smoke width fan-out, API --durations. Memory: none applied.