feat(audit): fit the audit tools into the agent surface (P8)

After P5 merged first: a close leads to the audit and the period's
attestation, an audit run to its workpaper and the claims behind it, the
attest tools to the attestations and the CPA package; a refusal for want of
a standing audit is the guard audit_required with books.audit as its
remedy; the audit prompt runs the audit tools. policy.cpa_package_requires_audit,
unset, refuses once the books hold an audit run and warns before, so a
book that has not begun the programme is not stopped from its first handoff
by a rule it has not met; set to refuse, it holds from the start.
bookspec states B-45 (convention) in its checker.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HS8WZziDnyxunC23MUxrLp

docs/mcp-interface.md

@@ -2797,7 +2797,7 @@ effort, and a period attested on a year-level audit (`annual`,
 
 `books.export_cpa_package` gains `without_audit_reason?`: on books that
 declared `audits`, with `policy.cpa_package_requires_audit` at `refuse` (the
-default), the package is refused (`audit_required`) unless an audit with
+default once the books hold an audit run; before one it warns), the package is refused (`audit_required`) unless an audit with
 scope `cpa_handoff` or `full` stands at the current head with a period
 attested on it at the bar; a reason overrides the refusal and is journaled
 as a decision. Under `warn` the package is made and its `warnings` say so.