fix(notification-service): resolve NotificationService-014..018 — classify OAuth2 failures, fail on bad auth config, wire NotificationOptions fallback, disposable concurrency limiter

src/ScadaLink.NotificationService/NotificationOptions.cs

@@ -1,15 +1,26 @@
 namespace ScadaLink.NotificationService;
 
 /// <summary>
-/// Configuration options for the Notification Service.
-/// Most SMTP configuration is stored in the database (SmtpConfiguration entity).
-/// This provides fallback defaults and operational limits.
+/// Configuration options for the Notification Service, bound from the
+/// <c>ScadaLink:Notification</c> configuration section.
+///
+/// SMTP settings are primarily carried by the deployed <c>SmtpConfiguration</c>
+/// entity. NS-017: these values are the fallback used by
+/// <see cref="NotificationDeliveryService"/> when the corresponding
+/// <c>SmtpConfiguration</c> field is left unset (non-positive) on a partially
+/// deployed row — a value present on the row always takes precedence.
 /// </summary>
 public class NotificationOptions
 {
-    /// <summary>Default connection timeout for SMTP connections.</summary>
+    /// <summary>
+    /// Connection timeout (seconds) used when <c>SmtpConfiguration.ConnectionTimeoutSeconds</c>
+    /// is unset. Default 30s.
+    /// </summary>
     public int ConnectionTimeoutSeconds { get; set; } = 30;
 
-    /// <summary>Maximum concurrent SMTP connections.</summary>
+    /// <summary>
+    /// Maximum concurrent SMTP connections used when
+    /// <c>SmtpConfiguration.MaxConcurrentConnections</c> is unset. Default 5.
+    /// </summary>
     public int MaxConcurrentConnections { get; set; } = 5;
 }