fix: separate shadow and paper lifecycle evidence

[Pigbibi]

Summary

• Treat Shadow as the mandatory non-live forward channel and Paper as an optional target capability.
• Keep Shadow active when Paper is explicitly unsupported; retain fail-closed pause behavior when configured channels are unhealthy.
• Distinguish contract, synthetic, observed, and deployed evidence in the lifecycle matrix without granting promotion or trading authority.
• Mark legacy latest_signal plugin mount documentation as historical compatibility material.

Safety

No strategy parameters, deployment targets, broker credentials, order paths, or live permissions change.

Verification

• rtk pytest tests/test_forward_observation.py tests/test_forward_observation_receipt.py tests/test_lifecycle_matrix_runtime.py tests/test_build_lifecycle_matrix_script.py tests/test_strategy_lifecycle_matrix.py
• git diff --check