test(plugin): cover the running-execution delete conflict over HTTP #109

Problem Description

The DELETE endpoint's 409 for running executions without force (#94, PR #105) is covered only by service-level unit tests in DynamicJobLoaderServiceTest. No HTTP-level test asserts the status code and error envelope that GlobalExceptionHandler returns for JobUnloadConflictException on DELETE /jobs/definitions/{id}.

Proposed Solution

Add an integration test that exercises DELETE /jobs/definitions/{id} while the running-execution guard rejects the request, and asserts the 409 status, the error envelope fields, and that the definition, JAR, and registration remain.

Acceptance Criteria

• An HTTP-level test asserts 409 and the error envelope for a delete blocked by running executions.
• The test asserts that nothing was deleted or unregistered.
• The test is deterministic and does not depend on timing of real job executions.

Affected Area

Plugin lifecycle: job definition deletion tests

Out of Scope

• Changing delete behavior.

Additional Context

Follow-up to #94 / PR #105. Raised by the native review suggestion R3-no-http-running-conflict-test. Note: because JobExecutionAuditListener writes history when a job starts, reaching this path may require stubbing the history check; see the related force semantics follow-up.