Add libenclaveapp architecture diagrams

[jgowdy-godaddy]

Summary

• add text-based Mermaid diagrams for the main libenclaveapp architecture and flows
• cover workspace/crate boundaries, app-storage backend selection, encryption, signing, adapter integration types, WSL bridge delegation, and metadata/trust boundaries
• keep consuming app domain logic out of scope except where shown as caller examples

Files

• docs/diagrams/README.md
• docs/diagrams/workspace-context.mmd
• docs/diagrams/app-storage-backend-selection.mmd
• docs/diagrams/encryption-flow.mmd
• docs/diagrams/signing-flow.mmd
• docs/diagrams/adapter-integration-types.mmd
• docs/diagrams/wsl-bridge-flow.mmd
• docs/diagrams/metadata-trust-boundary.mmd

Validation

Rendered all Mermaid sources to SVG with Mermaid CLI using system Chrome:

mmdc -p <puppeteer-config-for-system-chrome> -i docs/diagrams/<diagram>.mmd -o <tmp>/<diagram>.svg