feat(mission): /mission/receive_reward stub (refresh-only, no decomp)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SVSim.EmulatedEntrypoint/Models/Dtos/Requests/Mission/MissionReceiveRewardRequest.cs

@@ -0,0 +1,17 @@
+using MessagePack;
+using System.Text.Json.Serialization;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Requests.Mission;
+
+/// <summary>
+/// INFERRED shape — the spec at docs/api-spec/endpoints/post-login/mission-receive-reward.md
+/// flags this as not present in the client decompilation. Almost certainly an id of the
+/// mission to claim.
+/// </summary>
+[MessagePackObject]
+public class MissionReceiveRewardRequest : BaseRequest
+{
+    [JsonPropertyName("id")]
+    [Key("id")]
+    public long Id { get; set; }
+}