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/proto/proto/zed.proto

@@ -49,7 +49,7 @@ message Envelope {
         GetDefinition get_definition = 32;
         GetDefinitionResponse get_definition_response = 33;
         GetDeclaration get_declaration = 237;
-        GetDeclarationResponse get_declaration_response = 238; // current max
+        GetDeclarationResponse get_declaration_response = 238;
         GetTypeDefinition get_type_definition = 34;
         GetTypeDefinitionResponse get_type_definition_response = 35;
 
@@ -130,6 +130,8 @@ message Envelope {
         GetPrivateUserInfoResponse get_private_user_info_response = 103;
         UpdateUserPlan update_user_plan = 234;
         UpdateDiffBase update_diff_base = 104;
+        AcceptTermsOfService accept_terms_of_service = 239;
+        AcceptTermsOfServiceResponse accept_terms_of_service_response = 240; // current max
 
         OnTypeFormatting on_type_formatting = 105;
         OnTypeFormattingResponse on_type_formatting_response = 106;
@@ -270,7 +272,7 @@ message Envelope {
         AddWorktreeResponse add_worktree_response = 223;
 
         GetLlmToken get_llm_token = 235;
-        GetLlmTokenResponse get_llm_token_response = 236; // current max
+        GetLlmTokenResponse get_llm_token_response = 236;
     }
 
     reserved 158 to 161;
@@ -1692,6 +1694,7 @@ message GetPrivateUserInfoResponse {
     string metrics_id = 1;
     bool staff = 2;
     repeated string flags = 3;
+    optional uint64 accepted_tos_at = 4;
 }
 
 enum Plan {
@@ -1703,6 +1706,12 @@ message UpdateUserPlan {
     Plan plan = 1;
 }
 
+message AcceptTermsOfService {}
+
+message AcceptTermsOfServiceResponse {
+    uint64 accepted_tos_at = 1;
+}
+
 // Entities
 
 message ViewId {

crates/proto/src/proto.rs

@@ -187,6 +187,8 @@ impl fmt::Display for PeerId {
 }
 
 messages!(
+    (AcceptTermsOfService, Foreground),
+    (AcceptTermsOfServiceResponse, Foreground),
     (Ack, Foreground),
     (AckBufferOperation, Background),
     (AckChannelMessage, Background),
@@ -409,6 +411,7 @@ messages!(
 );
 
 request_messages!(
+    (AcceptTermsOfService, AcceptTermsOfServiceResponse),
     (ApplyCodeAction, ApplyCodeActionResponse),
     (
         ApplyCompletionAdditionalEdits,