Test Suite Cleanup and CI Debugging

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.

PR #6841 is queued in the lane. CI: all 7 recent red test.yml runs were develop drift already fixed; 0 flaky. Removed 2 retired tests and an orphan helper, cut one vitest typing test 2.5s→0.6s. Every other lever measured and rejected (in PR). Memory: none applied.