feat(sms): make FromNumber optional — support Twilio Messaging-Service-only configs (UI-Med-2)

Code-review finding UI-Med-2: the design doc + delivery adapter treat FromNumber and
MessagingServiceSid as either-or, but the entity ctor, EF schema, UI and CLI all hard-
required FromNumber — so a Messaging-Service-only Twilio config (a normal production
setup) could not be created. Bring the implementation into line with the spec:

- Commons: SmsConfiguration.FromNumber -> string? (ctor fromNumber optional);
  UpdateSmsConfigCommand.FromNumber -> string?.
- ConfigurationDatabase: FromNumber.IsRequired(false) + migration SmsFromNumberOptional
  (ALTER COLUMN nullable, idempotent; Down backfills '' — harmless, MsgSid keeps it
  deliverable) + regenerated model snapshot.
- Transport: SmsConfigDto.FromNumber -> string? (round-trips a Messaging-Service-only config).
- CentralUI: form validation requires AccountSid + at-least-one-of(FromNumber, MsgSid);
  nullable create/edit paths; From-number help text.
- CLI: --from-number no longer Required; BuildUpdateSmsConfigCommand validates the either-or.
- Adapter: From branch null-forgiving (guarded by the existing incomplete-config check).

Tests: ManagementActor MsgSid-only persists null FromNumber; CLI MsgSid-only builds +
neither-throws + contract (--from-number not Required); CentralUI MsgSid-only save.

tests/ZB.MOM.WW.ScadaBridge.ManagementService.Tests/ManagementActorTests.cs

@@ -1705,6 +1705,34 @@ public class ManagementActorTests : TestKit, IDisposable
         Assert.Equal("ACnew", existing.AccountSid);
     }
 
+    [Fact]
+    public void UpdateSmsConfig_MessagingServiceSidOnly_PersistsNullFromNumber()
+    {
+        // UI-Med-2: a Twilio Messaging-Service-only config has no From number. The handler
+        // must accept and persist a null FromNumber alongside a MessagingServiceSid.
+        var notifRepo = Substitute.For<INotificationRepository>();
+        var existing = new Commons.Entities.Notifications.SmsConfiguration("ACold", "+15550000000")
+        {
+            Id = 1,
+            AuthToken = "old-secret",
+        };
+        notifRepo.GetAllSmsConfigurationsAsync(Arg.Any<CancellationToken>())
+            .Returns(new List<Commons.Entities.Notifications.SmsConfiguration> { existing });
+        _services.AddScoped(_ => notifRepo);
+
+        var actor = CreateActor();
+        var envelope = Envelope(
+            new UpdateSmsConfigCommand(1, "ACnew", FromNumber: null, MessagingServiceSid: "MGonly"),
+            "Administrator");
+
+        actor.Tell(envelope);
+
+        var response = ExpectMsg<ManagementSuccess>(TimeSpan.FromSeconds(5));
+        Assert.Equal(envelope.CorrelationId, response.CorrelationId);
+        Assert.Null(existing.FromNumber);
+        Assert.Equal("MGonly", existing.MessagingServiceSid);
+    }
+
     [Fact]
     public void CuratedHandlerFailure_SurfacesTheCuratedMessage()
     {