Review and fix test suites and CI failures

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 #6617 queued in lane: test.yml red fixed (mutedText), crumb-sweep flake fixed (3/120→0/240, induced), 2 stale tests deleted, 390px→448, Context router selftest promoted to quick. Deferred: migration-test retirement; main/dev deploy failures noted. Memory: used mem-18424; proposed 0.