collab: Push down plan changes to the client (#30447)

This PR makes it so we push down plan updates from the server when the
user's subscription changes.

Release Notes:

- N/A

crates/collab/src/api/billing.rs

@@ -1137,6 +1137,12 @@ async fn handle_customer_subscription_event(
             .await?;
     }
 
+    // When the user's subscription changes, push down any changes to their plan.
+    rpc_server
+        .update_plan_for_user(billing_customer.user_id)
+        .await
+        .trace_err();
+
     // When the user's subscription changes, we want to refresh their LLM tokens
     // to either grant/revoke access.
     rpc_server