Remote GitHub agent sessions cannot be dismissed from the Sessions list

seen by @TylerLeonhardt

**Description**
Remote GitHub agent sessions appear in VS Code's Sessions list, but they cannot be opened or marked as done. Selecting a session does nothing, and using Done leaves it in the list. The sessions can be archived from [GitHub Copilot Agents](https://github.com/copilot/agents), but that capability is not available from VS Code.

**Steps to reproduce**
* Have one or more remote GitHub agent sessions associated with the account.
* Open the Sessions list in VS Code.
* Click a remote session, or invoke Done on it.

**Actual**: Clicking the session and marking it as done have no visible effect, so the item remains permanently in the list.

**Expected**: Remote sessions should support being opened and dismissed/archived from VS Code. Until that is supported, sessions that cannot be acted on or dismissed should not be shown in the list.