Benign import cycles compile under the dynamic tier too; refusals narrow to the binding

- The dynamic-import subgraph judges back edges with the same admission engine as the static graph; its refusals now reach the build instead of being discarded with the discovery pass
- TDZ-shape reads and non-inert top levels refuse naming the binding or statement and its location, not the whole cycle
- Evaluation order stays Node's postorder with back edges as cache hits, pinned by the parity baselines