feat(rank-battle): RankBattleController shell + DTOs + routing smoke tests

Stands up the controller with all 13 rank-battle URL routes wired via
explicit absolute [HttpPost] attributes (multi-prefix family — can't ride
[Route(\"[controller]\")]). Real DoMatching / AiStart logic arrives in
later tasks; finish + telemetry + force-finish are returnable stubs as
of this task.

DTOs cover the request + response shapes per the spec. Note the
camelCase wire keys on AiBattlePlayerInfo (sleeveId, emblemId, ...) —
the AI battle subsystem uses camelCase, not the project-default
snake_case, per AIBattleStartTask.Parse's literal Keys.Contains lookups.

DoMatchingResponseDto.NodeServerUrl is non-nullable + always-emit (with
[JsonIgnore(Never)]) — matches Phase 2's TK2 fix because the client's
DoMatchingBase parser calls .ToString() without a Keys.Contains guard.

13 routing smoke tests confirm each URL resolves to the controller.

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

SVSim.EmulatedEntrypoint/Models/Dtos/RankBattle/DoMatchingResponseDto.cs

@@ -0,0 +1,37 @@
+using System.Text.Json.Serialization;
+using MessagePack;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.RankBattle;
+
+[MessagePackObject(keyAsPropertyName: true)]
+public sealed class DoMatchingResponseDto
+{
+    [JsonPropertyName("matching_state")]
+    [Key("matching_state")]
+    public int MatchingState { get; set; }
+
+    [JsonPropertyName("timeout_period")]
+    [Key("timeout_period")]
+    public int TimeoutPeriod { get; set; } = 60;
+
+    [JsonPropertyName("retry_period")]
+    [Key("retry_period")]
+    public int RetryPeriod { get; set; } = 3;
+
+    [JsonPropertyName("battle_id")]
+    [Key("battle_id")]
+    public string? BattleId { get; set; }
+
+    // Always emitted, even on RETRY. Client's DoMatchingBase.SettingDoMatchingData()
+    // calls .ToString() on this without a Keys.Contains guard, so absence throws
+    // KeyNotFoundException before the matching_state switch runs. Same Phase 2 fix
+    // pattern as TK2.
+    [JsonPropertyName("node_server_url")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
+    [Key("node_server_url")]
+    public string NodeServerUrl { get; set; } = "";
+
+    [JsonPropertyName("card_master_id")]
+    [Key("card_master_id")]
+    public int? CardMasterId { get; set; }
+}