v0.2.0 — JSON object walker: whole-record compression for items[] shapes

compressEnvelope generalizes into a depth-limited JSON object walker: large string fields decode and recurse (runner envelopes whose stdout holds a JSON object), large array fields get whole-record row selection (kubectl-style {"items": [...]} — anomalous records survive intact, the rest offload as a retrievable array of complete records), large object fields recurse with a valid-JSON splice guard. Measured on a 251KB kubectl get pods -o json envelope: 62,754 → 1,498 tokens (97.6%) with the CrashLoopBackOff pod record kept whole.