Secrets manager integration (Vault/AWS)

[yaront1111]

Repo: cordum

Problem

SECURITY.md claims integration with Vault and AWS Secrets Manager, but OSS only detects secret refs.

Proposed

• Add secret resolver interface and providers for Vault and AWS Secrets Manager.
• Expose helper APIs for workers/gateway to resolve secret:// refs.

Acceptance

• secret://vault/... and secret://aws-sm/... resolve when configured.
• Docs updated with env vars and IAM requirements.
• Tests cover ref parsing and failure modes.

References

• core/infra/secrets/secrets.go
• SECURITY.md
• docs/CORE.MD