chore(udt-011): register DateOnlyJsonConverter in Program.cs AddJsonOptions

tests/SIGCM2.Api.Tests/Admin/FiscalControllerTests.cs

@@ -693,4 +693,46 @@ public sealed class FiscalControllerTests : IAsyncLifetime
         Assert.True(json.TryGetProperty("items", out _), "Response must have 'items'");
         Assert.True(json.TryGetProperty("total", out _), "Response must have 'total'");
     }
+
+    // ── UDT-011: DateOnly serialization format ────────────────────────────────
+
+    /// <summary>
+    /// [UDT-011 REQ-BE-JSON-001] POST /iva → vigenciaDesde en respuesta debe ser
+    /// "yyyy-MM-dd" (e.g. "2025-01-01"), no "2025-01-01T00:00:00" ni con sufijo "Z".
+    /// Valida que DateOnlyJsonConverter está activo en el pipeline de controllers.
+    /// </summary>
+    [Fact]
+    public async Task CreateIva_VigenciaDesde_SerializesAsDateOnlyString()
+    {
+        const string codigo = "IVA_9999";
+        var token = await GetAdminTokenAsync();
+        try
+        {
+            using var req = BuildRequest(HttpMethod.Post, IvaEndpoint, new
+            {
+                codigo,
+                descripcion = "IVA DateOnly Format Test",
+                porcentaje = 5.0m,
+                aplicaIVA = true,
+                vigenciaDesde = "2025-01-01"
+            }, token);
+            var resp = await _client.SendAsync(req);
+
+            Assert.Equal(HttpStatusCode.Created, resp.StatusCode);
+
+            // Read raw JSON string to inspect format (not deserialized)
+            var rawJson = await resp.Content.ReadAsStringAsync();
+
+            // vigenciaDesde MUST be "2025-01-01" — short date format
+            Assert.Contains("\"2025-01-01\"", rawJson);
+
+            // Must NOT contain datetime format or UTC suffix
+            Assert.DoesNotContain("T00:00:00", rawJson);
+            Assert.DoesNotContain("\"2025-01-01Z\"", rawJson);
+        }
+        finally
+        {
+            await DeleteTipoDeIvaByCodigoAsync(codigo);
+        }
+    }
 }