openapi: add Cloud-runtime fields workflow_id, execution_error to JobEntry

The Cloud runtime returns two additional fields on JobEntry that the spec
didn't declare:

- workflow_id: UUID of the Cloud workflow entity the job is associated with
- execution_error: structured ComfyUI execution error for failed jobs
  (reuses the existing ExecutionError schema)

Both tagged x-runtime: [cloud] with [cloud-only] descriptions; local ComfyUI
does not populate them.

openapi.yaml

@@ -7565,6 +7565,16 @@ components:
         outputs_count:
           type: integer
           description: Total number of output files
+        workflow_id:
+          type: string
+          nullable: true
+          x-runtime: [cloud]
+          description: "[cloud-only] UUID of the Cloud workflow entity this job is associated with. Local ComfyUI returns null."
+        execution_error:
+          x-runtime: [cloud]
+          description: "[cloud-only] Detailed execution error from ComfyUI for failed jobs. Absent on local ComfyUI."
+          allOf:
+            - $ref: "#/components/schemas/ExecutionError"
 
     JobDetailResponse:
       type: object