Concept for cross context operations

### What

For use cases like CSR we need a cross context operation support between certificate and crypto i.e., certificate signing using a private key. This task is to create a concept for support of such use cases.

### Acceptance Criteria (DoD)

1. Concept for cross context operations available
2. Epic or task for next steps available

### How

_No response_

No files, tests, or entry points are identified. Start by reviewing how certificate and crypto contexts are organized in the repository, then define the cross-context operation concept and record concrete next steps as an epic or task; done means both acceptance criteria are available.

Written by the indexing model from the issue text.