feat(replay): add /replay/info and /replay/detail DTOs

All numeric fields on ReplayInfoItemDto ship as string — matches prod
capture (frame 96 of traffic_prod_misc_clicking.ndjson). api-spec doc
will be updated separately.

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

SVSim.EmulatedEntrypoint/Models/Dtos/Replay/ReplayInfoResponseDto.cs

@@ -0,0 +1,18 @@
+using System.Text.Json.Serialization;
+using MessagePack;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Replay;
+
+[MessagePackObject]
+public sealed class ReplayInfoResponseDto
+{
+    /// <summary>
+    /// Required — client does not guard with Keys.Contains. Emit empty list, never null.
+    /// </summary>
+    [JsonPropertyName("replay_list"), Key("replay_list")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
+    public List<ReplayInfoItemDto> ReplayList { get; set; } = new();
+
+    // feature_maintenance_list intentionally omitted — optional per spec, never set
+    // because we don't gate replay viewing. WhenWritingNull drops it from the wire.
+}