Secret Suites Rotate

Rotate a secret suite: bump suite_version for every task in it.

Rotation makes a leaked answer go stale — runs recorded under the old version keep their recorded version (the run snapshots it at finalize), so a builder who memorised the previous answers gets no credit on the new version. Operator-driven (no automatic rotation). 404 when the suite has no tasks (so a typo'd suite_id can't silently no-op).