Make rollback monitoring proposal-only

[Pigbibi]

Summary

• replace false rolled_back evidence with an auditable rollback_proposed stage
• retain the legacy rollback() entry point as a no-execution compatibility alias
• make owner authorization explicit and record against the configured audit store

Safety

This change has no broker, deployment, runtime-target, or order adapter. It does not execute a rollback; it only records a proposal for owner-authorized platform controls.

Validation

• uv run --extra dev pytest tests/test_rollback_manager.py tests/test_lifecycle_contracts.py -q (22 passed)
• git diff --check