[FR-0006] Implement core credential issuance logic #13
Description
Implement the minimal logic required for issuing digital credentials to subjects (users, organizations). Create backend handlers supporting creation, signing, and secure storage of a simple credential type, with stubs or mocks for cryptographic operations if full implementation is not ready.
Definition of Ready:
- This issue is labeled with FR-0006 and 'status:Backlog'.
- At least one basic credential schema specified (or stub).
- Task is sized for a single backend developer.
Definition of Done:
- Endpoint or function accepts credential data, signs (or mocks signing) and stores it securely.
- Code supports retrieval for the 'holder' later.
- Handler is covered by at least one test.
- Readme updated with usage or test instructions.
- Product Owner review/accepts behavior.