Add more documentation around Guardians security models and common failures

### TL;DR

Amend existing documentation to expand on Guardians security model, common failures, and thoughts around each for security.

### Detailed design

_No response_

### Alternatives considered

_No response_

### Additional information

_No response_

Find the existing documentation about Guardians security models, likely in a docs/ directory or README. Look for sections on security models and common failures. Identify gaps where explanations can be expanded. Review the codebase to understand the security architecture and typical failure modes to inform the documentation additions.

Written by the indexing model from the issue text.