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.CLI.Tests/Commands/NotificationSmsCommandTests.cs

@@ -208,11 +208,37 @@ public class NotificationSmsCommandTests
     public void SmsUpdate_OptionalFlags_AreNotRequired()
     {
         var update = SmsUpdate();
+        Assert.False(update.Options.Single(o => o.Name == "--from-number").Required);
         Assert.False(update.Options.Single(o => o.Name == "--messaging-service-sid").Required);
         Assert.False(update.Options.Single(o => o.Name == "--api-base-url").Required);
         Assert.False(update.Options.Single(o => o.Name == "--auth-token").Required);
     }
 
+    [Fact]
+    public void SmsUpdate_MessagingServiceSidOnly_NoFromNumber_Builds()
+    {
+        // Twilio Messaging-Service-only config: From number omitted, Messaging Service SID
+        // supplied. The either-or validation accepts it and FromNumber maps to null.
+        var parse = Parse(SmsUpdate(),
+            "--id", "3", "--account-sid", "ACmsg", "--messaging-service-sid", "MGonly");
+
+        Assert.Empty(parse.Errors);
+        var cmd = NotificationCommands.BuildUpdateSmsConfigCommand(parse);
+
+        Assert.Null(cmd.FromNumber);
+        Assert.Equal("MGonly", cmd.MessagingServiceSid);
+    }
+
+    [Fact]
+    public void SmsUpdate_NeitherFromNorMessagingService_Throws()
+    {
+        // Neither sender identity supplied => the build rejects it so an SMS config is
+        // never left with no way to send (mirrors the UI + delivery-adapter validation).
+        var parse = Parse(SmsUpdate(), "--id", "4", "--account-sid", "ACnone");
+
+        Assert.Throws<ArgumentException>(() => NotificationCommands.BuildUpdateSmsConfigCommand(parse));
+    }
+
     [Fact]
     public void SmsCommands_ResolveViaRegistry()
     {