Elements Connect fields exported as stored key instead of displayed label inside TestExecutions[n] iterator

Summary

When an Elements Connect (nFeed) custom field is referenced from inside a
TestExecutions[n] iterator on a Test Plan export, Xporter outputs the
stored key instead of the displayed label. The same field exported
directly from the Test Execution issue is rendered correctly.

Steps to reproduce

1. Configure an EC custom field with stored value != displayed value.
2. On a Test Plan, link Test Executions that use that field.
3. Use a template with ${TestExecutions[n].<EC field>[id]}.
4. Export the Test Plan.
5. As a control, export one of the Test Executions directly with ${<EC field>}.

Expected

Both exports render the EC field with its displayed label.

Actual

• Top-level Test Execution export → displayed label (OK).
• Test Plan export via TestExecutions[n] → stored key.