[MugdhoAI]

Purpose

Add a compact visual at the top of the README that communicates the Vault API concept before readers reach the detailed architecture section.

Design

• A central vault node represents the authenticated secret API.
• A row of data elements suggests data moving through the service.
• PostgreSQL is shown as the persistence layer, with the diagram explicitly labeling Fernet encryption at rest.
• Use GitHub-rendered Mermaid rather than creating or adding another image asset.

Scope

README only. No application behavior, security guarantees, or deployment claims are changed.