XY-523: Expose private execution evidence in operator and agent handoff views

[yvette-carlisle]

Summary

• Add decodex evidence for local private execution evidence readback by issue, run, and attempt.
• Add compact private evidence refs to agent capsules, handoff index entries, and operator status rows without copying raw transcripts to public trackers.
• Document the local readback workflow for operators and future repair agents.

Validation

• cargo make fmt
• cargo make lint-fix
• cargo make test
• git diff --check
• Semantic drift audit against CLI/runtime/status/docs claims