Create vault audit evidence index

[El-swaggerito]

Description

Difficulty: Expert

Type: Documentation

Summary

Create an audit evidence index that organises all security-relevant vault documentation and tests.

Current Behaviour

Security reviewers need quick access to invariants, public API docs, storage maps, threat models, event schemas, and test coverage.

Expected Behaviour

The repository should provide one audit index that links all evidence and identifies gaps.

Suggested Implementation

Create an audit evidence index covering custody, accounting, storage, authorisation, events, errors, admin controls, migration assumptions, and test coverage.

Files or Areas Likely Affected

• docs/
• README.md
• tests/

Acceptance Criteria

• Audit evidence index is added.
• Invariant docs are linked.
• Storage and API docs are linked.
• Threat models are linked.
• Relevant tests are linked.
• Known audit gaps are listed.

Additional Notes

This should be honest about incomplete areas.