XY-871: Add Authority Envelope and Boundary Check for loop recovery

[yvette-carlisle]

Summary

• Define the Authority Envelope and Authority Boundary Check contract in loop/runtime/evidence docs.
• Add structured private authority_boundary_check event types and persistence helper.
• Feed sanitized authority-boundary failure signals into harness improvement candidates and private evidence readback.
• Extend loop scenario, agent evidence, and harness tests for requires-human/insufficient-evidence paths and payload non-leakage.

Validation

• cargo test -p decodex loop_scenario --all-features
• cargo test -p decodex agent_evidence --all-features
• cargo test -p decodex harness --all-features
• cargo make fmt
• cargo make lint-fix
• cargo make test (1025 passed, 1 skipped)