Add end-to-end auth and authorization regression tests

## Objective

Add end-to-end auth and authorization regression tests for issuer registration, publishing, updating, and cross-issuer denial.

## Context

The code has unit tests and demo notebooks for important flows, but the auth hardening work should have reliable automated coverage that runs in CI and protects against regressions.

## Deliverables

- [ ] Add integration tests for unregistered issuer publish/update denial.
- [ ] Add tests for issuer A attempting to update issuer B's status list.
- [ ] Add tests for credential registration/rotation rules after those are defined.
- [ ] Add tests for malformed Authorization headers and invalid JWTs at the router level.
- [ ] Ensure tests run under the default in-memory feature profile.

## Acceptance Criteria

- [ ] Auth regressions fail CI without requiring Docker or external services.
- [ ] Tests cover both `PUT` and `PATCH` management endpoints.
- [ ] Tests assert HTTP status and response body shape where stable.

## Verification

- [ ] `cargo nextest run --workspace --all-targets --features memory`

Start by locating the existing integration/router tests for issuer management endpoints, then run `cargo nextest run --workspace --all-targets --features memory` to establish baseline behavior. Add regression cases for unregistered issuer publish/update denial, cross-issuer update attempts, and malformed `Authorization` / invalid JWT handling on management routes for both PUT and PATCH. Assert expected HTTP status and stable response-body shape where available, and rerun the same nextest command to verify the new coverage passes in the default in-memory profile.

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