assistant: Require user to accept TOS for cloud provider (#16111)

This adds the requirement for users to accept the terms of service the
first time they send a message with the Cloud provider.

Once this is out and in a nightly, we need to add the check to the
server side too, to authenticate access to the models.

Demo:


https://github.com/user-attachments/assets/0edebf74-8120-4fa2-b801-bb76f04e8a17



Release Notes:

- N/A

crates/client/src/test.rs

@@ -1,5 +1,6 @@
 use crate::{Client, Connection, Credentials, EstablishConnectionError, UserStore};
 use anyhow::{anyhow, Result};
+use chrono::Duration;
 use futures::{stream::BoxStream, StreamExt};
 use gpui::{BackgroundExecutor, Context, Model, TestAppContext};
 use parking_lot::Mutex;
@@ -162,6 +163,11 @@ impl FakeServer {
                 return Ok(*message.downcast().unwrap());
             }
 
+            let accepted_tos_at = chrono::Utc::now()
+                .checked_sub_signed(Duration::hours(5))
+                .expect("failed to build accepted_tos_at")
+                .timestamp() as u64;
+
             if message.is::<TypedEnvelope<GetPrivateUserInfo>>() {
                 self.respond(
                     message
@@ -172,6 +178,7 @@ impl FakeServer {
                         metrics_id: "the-metrics-id".into(),
                         staff: false,
                         flags: Default::default(),
+                        accepted_tos_at: Some(accepted_tos_at),
                     },
                 );
                 continue;