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.Commons/Entities/Notifications/NotificationRecipient.cs

@@ -71,8 +71,9 @@ public class NotificationRecipient
     }
 
     /// <summary>
-    /// Parameterless constructor used by EF Core materialization and the SMS factory, where the
-    /// contact field is assigned via property setters rather than constructor parameters.
+    /// Private parameterless constructor that backs the <see cref="ForSms"/> factory path,
+    /// where the contact field is assigned via property setters rather than constructor
+    /// parameters — without exposing a half-initialized public constructor to callers.
     /// </summary>
     private NotificationRecipient()
     {

src/ZB.MOM.WW.ScadaBridge.Commons/Entities/Notifications/SmsConfiguration.cs

@@ -6,7 +6,10 @@ public class SmsConfiguration
     public int Id { get; set; }
     /// <summary>Gets or sets the Twilio Account SID.</summary>
     public string AccountSid { get; set; }
-    /// <summary>Gets or sets the Twilio Auth Token (secret), or null when not applicable.</summary>
+    /// <summary>
+    /// Gets or sets the Twilio Auth Token (secret). Stored encrypted; null only transiently
+    /// during configuration, never a valid production value.
+    /// </summary>
     public string? AuthToken { get; set; }
     /// <summary>Gets or sets the sender phone number (E.164) placed in the From field.</summary>
     public string FromNumber { get; set; }

src/ZB.MOM.WW.ScadaBridge.DeploymentManager/ArtifactDeploymentService.cs

@@ -179,7 +179,7 @@ public class ArtifactDeploymentService
 
         // Map notification lists
         var notificationListArtifacts = notificationLists.Select(nl =>
-            new NotificationListArtifact(nl.Name, nl.Recipients.Select(r => r.EmailAddress).ToList())).ToList();
+            new NotificationListArtifact(nl.Name, nl.Recipients.Where(r => r.EmailAddress is not null).Select(r => r.EmailAddress!).ToList())).ToList();
 
         // Map SMTP configurations — use Host as the artifact name (matches SQLite PK on site)
         var smtpArtifacts = smtpConfigurations.Select(smtp =>

src/ZB.MOM.WW.ScadaBridge.NotificationOutbox/Delivery/EmailNotificationDeliveryAdapter.cs

@@ -106,7 +106,10 @@ public sealed class EmailNotificationDeliveryAdapter : INotificationDeliveryAdap
             return DeliveryOutcome.Permanent(addressError);
         }
 
-        var recipientAddresses = recipients.Select(r => r.EmailAddress).ToList();
+        var recipientAddresses = recipients
+            .Where(r => r.EmailAddress is not null)
+            .Select(r => r.EmailAddress!)
+            .ToList();
 
         try
         {

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");

src/ZB.MOM.WW.ScadaBridge.Transport/Serialization/EntitySerializer.cs

@@ -138,9 +138,11 @@ public sealed class EntitySerializer
             NotificationLists: aggregate.NotificationLists.Select(nl => new NotificationListDto(
                 Name: nl.Name,
                 Type: nl.Type,
-                Recipients: nl.Recipients.Select(r => new NotificationRecipientDto(
-                    Name: r.Name,
-                    EmailAddress: r.EmailAddress)).ToList())).ToList(),
+                Recipients: nl.Recipients
+                    .Where(r => r.EmailAddress is not null)
+                    .Select(r => new NotificationRecipientDto(
+                        Name: r.Name,
+                        EmailAddress: r.EmailAddress!)).ToList())).ToList(),
             SmtpConfigs: aggregate.SmtpConfigurations.Select(smtp =>
             {
                 SecretsBlock? secrets = null;