mode/2up is ignored when rendering in iframe

**Description**

I am attempting to display an item embedded in an iframe, and I want it to start in 2up mode. I have an embed url which works correctly outside an iframe, but when it is used inside an iframe, it opens in 1up mode.

**Evidence / Screenshot (if possible)**

See https://www.wallandbinkley.com/poet/ . The iframe uses this url: https://archive.org/embed/p-c-programme-uaa-1995-131-636-002-2-1/page/0/mode/2up?ui=embed , but within the iframe the item is displayed in 1up mode. If you visit that url directly, it is displayed in 2up.

**Expectation**

Within the iframe the item should be displayed in 2up mode.

**Context**

Should work in any browser. I have tested in Firefox, Chrome and Edge in Windows 11, Firefox in Ubuntu, and Firefox in Android. All open the item in 1up mode. I don't see a reason why BookReader should behave differently in the iframe than it does in page called directly.

**Proposal & Constraints**

Let me know if the syntax of my embed url is wrong - otherwise fix BookReader to respect mode/2up when embedded inside an iframe

**Stakeholders**