[FA-55] User Service backend initial setup

FictionArchive.Service.UserService/Services/AuthenticationClient/Authentik/AuthentikAddUserRequest.cs

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+using System.Text.Json.Serialization;
+
+namespace FictionArchive.Service.UserService.Services.AuthenticationClient.Authentik;
+
+public class AuthentikAddUserRequest
+{
+    [JsonPropertyName("username")]
+    public required string Username { get; set; }
+
+    [JsonPropertyName("name")]
+    public required string DisplayName { get; set; }
+
+    [JsonPropertyName("email")]
+    public required string Email { get; set; }
+
+    [JsonPropertyName("is_active")]
+    public bool IsActive { get; set; } = true;
+
+    [JsonPropertyName("type")]
+    public string Type { get; } = "external";
+}

FictionArchive.Service.UserService/Services/AuthenticationClient/Authentik/AuthentikClient.cs

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+using System.Net.Http.Json;
+
+namespace FictionArchive.Service.UserService.Services.AuthenticationClient.Authentik;
+
+public class AuthentikClient : IAuthenticationServiceClient
+{
+    private readonly HttpClient _httpClient;
+    private readonly ILogger<AuthentikClient> _logger;
+
+    public AuthentikClient(HttpClient httpClient, ILogger<AuthentikClient> logger)
+    {
+        _httpClient = httpClient;
+        _logger = logger;
+    }
+
+    public async Task<AuthentikUserResponse?> CreateUserAsync(string username, string email, string displayName)
+    {
+        var request = new AuthentikAddUserRequest
+        {
+            Username = username,
+            Email = email,
+            DisplayName = displayName,
+            IsActive = true
+        };
+
+        try
+        {
+            var response = await _httpClient.PostAsJsonAsync("/api/v3/core/users/", request);
+
+            if (!response.IsSuccessStatusCode)
+            {
+                var errorContent = await response.Content.ReadAsStringAsync();
+                _logger.LogError(
+                    "Failed to create user in Authentik. Status: {StatusCode}, Error: {Error}",
+                    response.StatusCode, errorContent);
+                return null;
+            }
+
+            var userResponse = await response.Content.ReadFromJsonAsync<AuthentikUserResponse>();
+            _logger.LogInformation("Successfully created user {Username} in Authentik with pk {Pk}",
+                username, userResponse?.Pk);
+
+            return userResponse;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Exception while creating user {Username} in Authentik", username);
+            return null;
+        }
+    }
+
+    public async Task<bool> SendRecoveryEmailAsync(int authentikUserId)
+    {
+        try
+        {
+            var response = await _httpClient.PostAsync(
+                $"/api/v3/core/users/{authentikUserId}/recovery_email/",
+                null);
+
+            if (!response.IsSuccessStatusCode)
+            {
+                var errorContent = await response.Content.ReadAsStringAsync();
+                _logger.LogError(
+                    "Failed to send recovery email for user {UserId}. Status: {StatusCode}, Error: {Error}",
+                    authentikUserId, response.StatusCode, errorContent);
+                return false;
+            }
+
+            _logger.LogInformation("Successfully sent recovery email to Authentik user {UserId}", authentikUserId);
+            return true;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Exception while sending recovery email to Authentik user {UserId}", authentikUserId);
+            return false;
+        }
+    }
+}

FictionArchive.Service.UserService/Services/AuthenticationClient/Authentik/AuthentikConfiguration.cs

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+namespace FictionArchive.Service.UserService.Services.AuthenticationClient.Authentik;
+
+public class AuthentikConfiguration
+{
+    public string BaseUrl { get; set; } = string.Empty;
+    public string ApiToken { get; set; } = string.Empty;
+}

FictionArchive.Service.UserService/Services/AuthenticationClient/Authentik/AuthentikUserResponse.cs

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+using System.Text.Json.Serialization;
+
+namespace FictionArchive.Service.UserService.Services.AuthenticationClient.Authentik;
+
+public class AuthentikUserResponse
+{
+    [JsonPropertyName("pk")]
+    public int Pk { get; set; }
+
+    [JsonPropertyName("username")]
+    public string Username { get; set; } = string.Empty;
+
+    [JsonPropertyName("name")]
+    public string Name { get; set; } = string.Empty;
+
+    [JsonPropertyName("email")]
+    public string Email { get; set; } = string.Empty;
+
+    [JsonPropertyName("is_active")]
+    public bool IsActive { get; set; }
+
+    [JsonPropertyName("is_superuser")]
+    public bool IsSuperuser { get; set; }
+
+    [JsonPropertyName("uid")]
+    public string Uid { get; set; } = string.Empty;
+}

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

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+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);
+}