[FA-55] User Service backend initial setup

FictionArchive.Service.UserService/Services/AuthenticationClient/IAuthenticationServiceClient.cs

@@ -0,0 +1,22 @@
+using FictionArchive.Service.UserService.Services.AuthenticationClient.Authentik;
+
+namespace FictionArchive.Service.UserService.Services.AuthenticationClient;
+
+public interface IAuthenticationServiceClient
+{
+    /// <summary>
+    /// Creates a new user in the authentication provider.
+    /// </summary>
+    /// <param name="username">The username for the new user</param>
+    /// <param name="email">The email address for the new user</param>
+    /// <param name="displayName">The display name for the new user</param>
+    /// <returns>The created user response, or null if creation failed</returns>
+    Task<AuthentikUserResponse?> CreateUserAsync(string username, string email, string displayName);
+
+    /// <summary>
+    /// Sends a password recovery email to the user.
+    /// </summary>
+    /// <param name="authentikUserId">The Authentik user ID (pk)</param>
+    /// <returns>True if the email was sent successfully, false otherwise</returns>
+    Task<bool> SendRecoveryEmailAsync(int authentikUserId);
+}