[Guests] Live share updates for guests #3818

User Story

As a guest, I want my view to update when my share is changed or removed, so that I always see what I can actually do.

User Value

Guests aren't confronted with outdated permissions or failing actions after the sharer changed or revoked their access.

Acceptance Criteria

• When the sharer changes the guest's role, the guest's file list reloads with the new permissions
• When the sharer removes the share, the guest sees a message that their access was revoked
• Share events for other users inside the guest's share don't trigger these updates

Notes

Web only. The server already sends share-updated and share-removed to guests, with the guest's id (email) in affecteduserids. The SSE share handlers check userStore.user.id, which doesn't exist for guests. The guest's id can be taken from the share permissions in sharedWithMe.