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

Cargo.lock

@@ -16537,6 +16537,7 @@ dependencies = [
  "call",
  "chrono",
  "client",
+ "cloud_llm_client",
  "collections",
  "db",
  "gpui",