fix(sms): repair S1 build breaks — null-filter EmailAddress projections + SiteNotificationRepository SMS stubs

S1 made NotificationRecipient.EmailAddress nullable + added SmsConfiguration
and four INotificationRepository SMS methods, breaking compilation beyond the
intentionally-deferred central NotificationRepository.

Fix 1 (CS8620/CS8604 nullable EmailAddress projections, email-only paths):
- NotificationOutbox EmailNotificationDeliveryAdapter: filter non-null emails
- DeploymentManager ArtifactDeploymentService: filter non-null emails
- Transport EntitySerializer: filter non-null emails into NotificationRecipientDto

Fix 2 (CS0535): stub the four SMS-config methods on SiteRuntime
SiteNotificationRepository (central-only — NotSupportedException, matching the
existing 'Managed via artifact deployment from Central' write-path pattern).

Doc nits: reword NotificationRecipient private ctor and SmsConfiguration.AuthToken
comments.

The central ConfigurationDatabase.NotificationRepository compile break is left
as-is (S2 implements those four methods).

src/ZB.MOM.WW.ScadaBridge.SiteRuntime/Repositories/SiteNotificationRepository.cs

@@ -193,6 +193,24 @@ public class SiteNotificationRepository : INotificationRepository
     public Task DeleteSmtpConfigurationAsync(int id, CancellationToken cancellationToken = default)
         => throw new NotSupportedException("Managed via artifact deployment from Central");
 
+    // ── SmsConfiguration (central-only — never deployed to or served from the site) ──
+
+    /// <inheritdoc />
+    public Task<SmsConfiguration?> GetSmsConfigurationAsync(CancellationToken cancellationToken = default)
+        => throw new NotSupportedException("Managed via artifact deployment from Central");
+
+    /// <inheritdoc />
+    public Task<IReadOnlyList<SmsConfiguration>> GetAllSmsConfigurationsAsync(CancellationToken cancellationToken = default)
+        => throw new NotSupportedException("Managed via artifact deployment from Central");
+
+    /// <inheritdoc />
+    public Task AddSmsConfigurationAsync(SmsConfiguration smsConfiguration, CancellationToken cancellationToken = default)
+        => throw new NotSupportedException("Managed via artifact deployment from Central");
+
+    /// <inheritdoc />
+    public Task UpdateSmsConfigurationAsync(SmsConfiguration smsConfiguration, CancellationToken cancellationToken = default)
+        => throw new NotSupportedException("Managed via artifact deployment from Central");
+
     /// <inheritdoc />
     public Task<int> SaveChangesAsync(CancellationToken cancellationToken = default)
         => throw new NotSupportedException("Managed via artifact deployment from Central");