fix(replay-tests): supply BaseRequest auth fields in PostAsJsonAsync bodies

Following the 216dcab fix that added [FromBody] BaseRequest _ to the
Info action, the existing tests' empty new {} payloads no longer satisfy
[ApiController] model validation (BaseRequest.ViewerId is non-nullable
string). Use the same EmptyBody() shape as RankBattleControllerTests
to mirror the production wire.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

SVSim.UnitTests/Controllers/ReplayControllerTests.cs

@@ -11,6 +11,18 @@ namespace SVSim.UnitTests.Controllers;
 
 public class ReplayControllerTests
 {
+    // Minimal BaseRequest-shaped body. The translation middleware (in prod) and the
+    // [FromBody] BaseRequest _ binding (in tests) both require the auth fields to
+    // be present even when their values are unused — same pattern as
+    // RankBattleControllerTests.FinishBody. The actual viewer_id comes from the
+    // session claim, not the body.
+    private static object EmptyBody() => new
+    {
+        viewer_id = "0",
+        steam_id = 0,
+        steam_session_ticket = "",
+    };
+
     [Test]
     public async Task ReplayInfo_returns_empty_list_for_fresh_viewer()
     {
@@ -18,7 +30,7 @@ public class ReplayControllerTests
         long viewerId = await factory.SeedViewerAsync(steamId: 76_561_198_000_000_001UL);
         var client = factory.CreateAuthenticatedClient(viewerId);
 
-        var resp = await client.PostAsJsonAsync("/replay/info", new { });
+        var resp = await client.PostAsJsonAsync("/replay/info", EmptyBody());
         Assert.That(resp.StatusCode, Is.EqualTo(HttpStatusCode.OK));
 
         var body = await resp.Content.ReadFromJsonAsync<ReplayInfoResponseDto>();
@@ -42,7 +54,7 @@ public class ReplayControllerTests
         }
 
         var client = factory.CreateAuthenticatedClient(viewerId);
-        var body = await client.PostAsJsonAsync("/replay/info", new { })
+        var body = await client.PostAsJsonAsync("/replay/info", EmptyBody())
             .ContinueWith(t => t.Result.Content.ReadFromJsonAsync<ReplayInfoResponseDto>())
             .Unwrap();
 
@@ -66,7 +78,7 @@ public class ReplayControllerTests
         }
 
         var client = factory.CreateAuthenticatedClient(viewerA);
-        var body = await client.PostAsJsonAsync("/replay/info", new { })
+        var body = await client.PostAsJsonAsync("/replay/info", EmptyBody())
             .ContinueWith(t => t.Result.Content.ReadFromJsonAsync<ReplayInfoResponseDto>())
             .Unwrap();