feat: Add main application views and structure

- Implemented CreateInstanceView for creating new instances.
- Added HostsView for managing SSH hosts with CRUD operations.
- Created InstancesView for displaying and managing instances.
- Developed LogsView for viewing operation logs.
- Introduced SecretsView for managing secrets associated with hosts.
- Established SettingsView for configuring application settings.
- Created MainWindow as the main application window with navigation.
- Added app manifest and configuration files for logging and settings.

OTSSignsOrchestrator.Core/Services/XiboApiService.cs

@@ -0,0 +1,90 @@
+using Microsoft.Extensions.Logging;
+using Microsoft.Extensions.Options;
+using OTSSignsOrchestrator.Core.Configuration;
+
+namespace OTSSignsOrchestrator.Core.Services;
+
+/// <summary>
+/// Tests connectivity to deployed Xibo CMS instances using OAuth2.
+/// </summary>
+public class XiboApiService
+{
+    private readonly IHttpClientFactory _httpClientFactory;
+    private readonly XiboOptions _options;
+    private readonly ILogger<XiboApiService> _logger;
+
+    public XiboApiService(
+        IHttpClientFactory httpClientFactory,
+        IOptions<XiboOptions> options,
+        ILogger<XiboApiService> logger)
+    {
+        _httpClientFactory = httpClientFactory;
+        _options = options.Value;
+        _logger = logger;
+    }
+
+    public async Task<XiboTestResult> TestConnectionAsync(string instanceUrl, string username, string password)
+    {
+        _logger.LogInformation("Testing Xibo connection to {InstanceUrl}", instanceUrl);
+
+        var client = _httpClientFactory.CreateClient("XiboApi");
+        client.Timeout = TimeSpan.FromSeconds(_options.TestConnectionTimeoutSeconds);
+
+        try
+        {
+            var baseUrl = instanceUrl.TrimEnd('/');
+            var tokenUrl = $"{baseUrl}/api/authorize/access_token";
+
+            var formContent = new FormUrlEncodedContent(new[]
+            {
+                new KeyValuePair<string, string>("grant_type", "client_credentials"),
+                new KeyValuePair<string, string>("client_id", username),
+                new KeyValuePair<string, string>("client_secret", password)
+            });
+
+            var response = await client.PostAsync(tokenUrl, formContent);
+
+            if (response.IsSuccessStatusCode)
+            {
+                _logger.LogInformation("Xibo connection test succeeded for {InstanceUrl}", instanceUrl);
+                return new XiboTestResult
+                {
+                    IsValid = true,
+                    Message = "Connected successfully.",
+                    HttpStatus = (int)response.StatusCode
+                };
+            }
+
+            _logger.LogWarning("Xibo connection test failed: {InstanceUrl} | status={StatusCode}",
+                instanceUrl, (int)response.StatusCode);
+
+            return new XiboTestResult
+            {
+                IsValid = false,
+                Message = response.StatusCode switch
+                {
+                    System.Net.HttpStatusCode.Unauthorized => "Invalid Xibo credentials.",
+                    System.Net.HttpStatusCode.Forbidden => "User lacks API permissions.",
+                    System.Net.HttpStatusCode.ServiceUnavailable => "Xibo instance not ready.",
+                    _ => $"Unexpected response: {(int)response.StatusCode}"
+                },
+                HttpStatus = (int)response.StatusCode
+            };
+        }
+        catch (TaskCanceledException)
+        {
+            return new XiboTestResult { IsValid = false, Message = "Connection timed out." };
+        }
+        catch (HttpRequestException ex)
+        {
+            return new XiboTestResult { IsValid = false, Message = $"Cannot reach Xibo instance: {ex.Message}" };
+        }
+    }
+}
+
+public class XiboTestResult
+{
+    public bool IsValid { get; set; }
+    public string Message { get; set; } = string.Empty;
+    public int HttpStatus { get; set; }
+}