feat(crosscheck): add R6 SHA addendum and status

[ruby-dlee]

Summary

• Append the exact full-SHA reproduction requirement only for non-Codex reviewer families while preserving the Codex prompt bytes.
• Add a read-only status command for serving family, same-model policy, and latest durable review family.
• Keep the existing full-SHA verdict gate intact and mutation-pinned.
• Accept validated historical ledger directory renames without weakening ledger schema, bounds, or symlink checks.

Verification

• tests/run.sh tests/fm-crosscheck.test.sh
• bin/fm-lint.sh (251 scripts)
• tests/run.sh tests/fm-crosscheck-azure.test.sh
• focused prompt, verdict-gate, reviewer, fallback, and status cases
• Python compilation and diff checks
• real operator-home status smoke

Bootstrap review

This PR uses the documented one-time local bootstrap review with same-model enabled, then restores the operator policy to off immediately. The review ledger records that degraded family mode.

[ruby-dlee]

bugbot run