Ability to duplicate Pages

### User Story
As a form builder
I need to copy all of the questions on a page
When I am building a section that has similar answers
So that I can save time

Feedback: being able to copy/duplicate questions across pages would be great

### Support tickets:
- https://cds-snc.freshdesk.com/a/tickets/18728
- https://cds-snc.freshdesk.com/a/tickets/24695
- https://cds-snc.freshdesk.com/a/tickets/27705

Start by locating the page and question-building entry points in the TypeScript/Next.js client and trace how a page’s questions are represented and persisted. Review the linked support-ticket context and existing page actions. Done means a form builder can duplicate all questions from one page into another, with the expected questions preserved and verified by the relevant tests.

Written by the indexing model from the issue text.