Hosted Codex runtime and backup tests fail while local tests pass

Symptom: Several Codex runtime tests fail together, and the history/backup tests report uv exiting 127 on the hosted Quality runner.

Root cause: These tests use uv to run Python validation. It was present on the developer machine and installed by Docker bootstrap, but absent from the separately provisioned hosted Quality environment.

Confirm: Check for Command not found on uv run in the Bats warnings. The fast test entrypoint now requires uv before it starts any fixtures.

Fix: Provision uv through the existing SHA-pinned validation-tool action. Its manifest pins uv’s version with the action revision. Keep the dependency check and real runtime/backup tests enabled.