feat(ranking): stub /ranking/* (6 endpoints)

Rankings menu opens. Period picker shows deterministic monthly schedule.
Every leaderboard returns { period, ranking: [] }.

Endpoints:
- /ranking/get_viewable_ranking_period_list
- /ranking/master_point_{rotation,unlimited}_info
- /ranking/rank_match_class_win_{rotation,unlimited}_info
- /ranking/two_pick_win_info

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

SVSim.EmulatedEntrypoint/Models/Dtos/Ranking/RankingEntryDto.cs

@@ -0,0 +1,44 @@
+using System.Text.Json.Serialization;
+using MessagePack;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Ranking;
+
+/// <summary>
+/// One row in a /ranking/* leaderboard's `ranking[]` array. Stub server never
+/// emits these; the type exists so the DTO compiles and so wire-shape tests can
+/// parse captured prod frames into it. Wire-type quirks (per capture frame 65):
+/// viewer_id/score/ranking_rank are STRINGS; rank/emblem_id/degree_id are NUMBERS.
+/// </summary>
+[MessagePackObject]
+public sealed class RankingEntryDto
+{
+    [JsonPropertyName("viewer_id"), Key("viewer_id")]
+    public string ViewerId { get; set; } = "0";
+
+    [JsonPropertyName("score"), Key("score")]
+    public string Score { get; set; } = "0";
+
+    [JsonPropertyName("ranking_rank"), Key("ranking_rank")]
+    public string RankingRank { get; set; } = "0";
+
+    [JsonPropertyName("name"), Key("name")]
+    public string Name { get; set; } = "";
+
+    [JsonPropertyName("country_code"), Key("country_code")]
+    public string CountryCode { get; set; } = "";
+
+    [JsonPropertyName("rank"), Key("rank")]
+    public int Rank { get; set; }
+
+    [JsonPropertyName("emblem_id"), Key("emblem_id")]
+    public long EmblemId { get; set; }
+
+    [JsonPropertyName("degree_id"), Key("degree_id")]
+    public long DegreeId { get; set; }
+
+    [JsonPropertyName("last_play_time"), Key("last_play_time")]
+    public string LastPlayTime { get; set; } = "";
+
+    [JsonPropertyName("guild_name"), Key("guild_name")]
+    public string GuildName { get; set; } = "";
+}