add check membership for chat proto

proto/chat/chat.proto

@@ -24,6 +24,8 @@ service ChatService {
   
   // Статусы
   rpc MarkAsRead(MarkAsReadRequest) returns (MarkAsReadResponse);
+
+  rpc CheckChatMembership(CheckChatMembershipRequest) returns (CheckChatMembershipResponse);
 }
 
 // --- СТРУКТУРЫ ДАННЫХ --- //
@@ -152,3 +154,13 @@ message MarkAsReadRequest {
   string message_id = 3; // ID последнего видимого сообщения
 }
 message MarkAsReadResponse { bool success = 1; }
+
+
+message CheckChatMembershipRequest {
+  string user_id = 1;
+  string chat_id = 2;
+}
+
+message CheckChatMembershipResponse {
+  bool is_member = 1;
+}