LOE needed - Activity pages for 3rd party users

It would be helpful to have a rough, high-level predicted level of effort for future work so that we (Dan, Arti, Andrew) can prioritize the upcoming work based on both business priority as well as predicted LOE.

Activity pages for 3rd party users: https://trello.com/c/1c0TywZE/47-give-3rd-party-users-access-to-activity-pages

Start with the linked Trello card, “Give 3rd party users access to activity pages,” and review its current scope and acceptance details. Identify the affected activity-page entry points and access-control behavior before estimating the work; done means producing a rough level-of-effort estimate for prioritization, not implementing the feature.

Written by the indexing model from the issue text.