If it's a lot of PRs indeed it's not super practical as you'd have to manually open each PR and send a message in the conversation to share the content of the page.
You wanted an assistant that have access at all time to all the opened PR of a repo? What is the use case to have access to multiple PRs at once? Just being curious
The idea would be to use an assistant to help on the review process, it would give warnings on best practices, internal naming conventions, coding conventions and suggests alternatives