test(csharp): fix 2 pre-existing failures from the #38 @required nullability change

Both stem from the #38 '@required CLR nullability' generator change (2026-06-17)
not propagating to committed fixtures + a test expectation:

- IntegrationFixtureDriftTests: regenerate the drifted committed integration
  fixtures — BridgeAuth.g.cs (int? Quantity → int Quantity) + Settings.g.cs
  (added a using directive the generator now emits).
- TphCodegenTests.Entity_subtypes_extend_base...: stale test expectation, NOT a
  generator bug — the generator correctly emits non-null int Quantity for a
  @required TPH-subtype field (EF auto-nullables the column); the test still
  asserted int?. Updated the expectation + comment to the #38 rationale.

Verified: dotnet test MetaObjects.sln — Render 290, Conformance 666, Cli 34,
Codegen 222 (0 failed); the regen harness stays Skip-gated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LuZWKnWzYGVnESijL7uuky

Author: dmealing

server/csharp/MetaObjects.Codegen.Tests/TphCodegenTests.cs

@@ -116,9 +116,11 @@ public void Entity_subtypes_extend_base_with_only_own_fields_and_no_table()
         var bridge = FileContent(files, "BridgeAuth.g.cs");
         Assert.Contains("public class BridgeAuth : Auth", bridge);
         Assert.DoesNotContain("[Table", bridge);
-        // Own field only — subtype column is nullable in the single table (EF folds it),
-        // so even an @required subtype field is emitted nullable.
-        Assert.Contains("public int? Quantity { get; set; }", bridge);
+        // Own field only. A @required subtype field is non-null in CLR (logically
+        // required); EF Core auto-nullables the underlying COLUMN for TPH-derived
+        // properties (a row of another subtype stores NULL there), so the non-null CLR
+        // type still maps to a nullable column correctly (#38, @required CLR nullability).
+        Assert.Contains("public int Quantity { get; set; }", bridge);
         // Inherited columns are NOT re-emitted on the subtype.
         Assert.DoesNotContain("public long Id", bridge);
         Assert.DoesNotContain("public string Reference", bridge);

server/csharp/MetaObjects.IntegrationTests/Generated/BridgeAuth.g.cs

@@ -11,5 +11,5 @@ namespace MetaObjects.IntegrationTests.Generated;
 public class BridgeAuth : Auth
 {
     [Column("quantity")]
-    public int? Quantity { get; set; }
+    public int Quantity { get; set; }
 }

server/csharp/MetaObjects.IntegrationTests/Generated/Settings.g.cs

@@ -3,6 +3,7 @@
 #nullable enable
 using System;
 using System.Collections.Generic;
+using System.ComponentModel.DataAnnotations.Schema;
 
 namespace MetaObjects.IntegrationTests.Generated;