Allow users to view and resume ongoing login sessions

[beubax]

What happened?

Login sessions currently exist in memory and can be resumed internally, but users do not have a clear way to see ongoing sessions or continue a login request from the UI. This is especially noticeable when an agent initiates authsome login <provider> and the human needs to complete or recover the flow later.

Because sessions are hidden from the user, an interrupted or backgrounded login flow can feel lost even if the session is technically still resumable.

What did you expect?

Users should be able to view ongoing login sessions and resume a pending login request when appropriate. The UI should make it clear which provider, identity, connection, and/or initiating agent the session belongs to, and should provide a safe way to continue or cancel the flow.

The sessions can remain in-memory for now. This issue is about exposing active resumable sessions to users and making the resume path usable, not necessarily making sessions durable across server restarts.

Steps to reproduce

1. Start a login flow from an agent, for example authsome login github.
2. Interrupt, background, or navigate away before completing the login.
3. Open the dashboard or relevant UI.
4. Observe that there is no obvious place to view the pending login session or continue it.
5. Add a UI/API path that lists active resumable sessions and lets the user continue or cancel a pending login request.