title_bar: Show the plan from the CloudUserStore (#35401)

This PR updates the user menu in the title bar to show the plan from the
`CloudUserStore` instead of the `UserStore`.

We're still leveraging the RPC connection to listen for `UpdateUserPlan`
messages so that we can get live-updates from the server, but we are
merely using this as a signal to re-fetch the information from Cloud.

Release Notes:

- N/A

crates/client/src/user.rs

@@ -145,6 +145,7 @@ pub enum Event {
     ShowContacts,
     ParticipantIndicesChanged,
     PrivateUserInfoUpdated,
+    PlanUpdated,
 }
 
 #[derive(Clone, Copy)]
@@ -388,6 +389,7 @@ impl UserStore {
                     .map(EditPredictionUsage);
             }
 
+            cx.emit(Event::PlanUpdated);
             cx.notify();
         })?;
         Ok(())