chore(udt-010): bootstrap rama + spike anti-MSDTC

Validates design decision #D-1 (TransactionScope ambient over IUnitOfWork):
TransactionScope with TransactionScopeAsyncFlowOption.Enabled does NOT
escalate to MSDTC when multiple SqlConnections share the same connection
string. Test passes (DistributedIdentifier == Guid.Empty).

Unblocks UDT-010 batches B1-B14.

Refs: sdd/udt-010-auditoria-trazabilidad/{design,tasks}

tests/SIGCM2.Api.Tests/Audit/TransactionScopeSpikeTests.cs

@@ -0,0 +1,58 @@
+using System.Transactions;
+using FluentAssertions;
+using Microsoft.Data.SqlClient;
+using Xunit;
+
+namespace SIGCM2.Api.Tests.Audit;
+
+/// UDT-010 Batch 0 — anti-MSDTC spike. Validates design decision #D-1:
+/// TransactionScope with AsyncFlowEnabled must NOT escalate to MSDTC when
+/// multiple SqlConnections share a single connection string. If this fails,
+/// UDT-010 must pivot to explicit IUnitOfWork.
+public sealed class TransactionScopeSpikeTests
+{
+    private const string ConnectionString =
+        "Server=TECNICA3;Database=SIGCM2_Test;User Id=desarrollo;Password=desarrollo2026;TrustServerCertificate=True;";
+
+    [Fact]
+    public async Task TransactionScope_DoesNotEscalateToMSDTC_WithSingleConnectionString()
+    {
+        var txOptions = new TransactionOptions
+        {
+            IsolationLevel = IsolationLevel.ReadCommitted
+        };
+
+        using var tx = new TransactionScope(
+            TransactionScopeOption.Required,
+            txOptions,
+            TransactionScopeAsyncFlowOption.Enabled);
+
+        await using (var conn1 = new SqlConnection(ConnectionString))
+        {
+            await conn1.OpenAsync();
+            using var cmd1 = conn1.CreateCommand();
+            cmd1.CommandText = "SELECT 1";
+            var result1 = await cmd1.ExecuteScalarAsync();
+            result1.Should().Be(1);
+        }
+
+        await using (var conn2 = new SqlConnection(ConnectionString))
+        {
+            await conn2.OpenAsync();
+            using var cmd2 = conn2.CreateCommand();
+            cmd2.CommandText = "SELECT 1";
+            var result2 = await cmd2.ExecuteScalarAsync();
+            result2.Should().Be(1);
+        }
+
+        var current = Transaction.Current;
+        current.Should().NotBeNull("TransactionScope must set an ambient transaction");
+        current!.TransactionInformation.DistributedIdentifier
+            .Should().Be(Guid.Empty,
+                "SQL Server with a single connection string must NOT escalate to MSDTC. " +
+                "If this assertion fails, UDT-010 design must pivot to explicit IUnitOfWork " +
+                "(see sdd/udt-010-auditoria-trazabilidad/design #D-1).");
+
+        tx.Complete();
+    }
+}