feat(rank-battle): AiStart returns ai_id + camelCase self/oppo_info

AiStartInternal builds the self MatchContext, picks a bot from
IBotRoster, projects to the AiBattleStartResponseDto with camelCase
wire keys (sleeveId, emblemId, ... — see ai-start.md). turnState=0
(player first) is the safe default per the ai-start.md TODO; live
capture would clarify the enum.

No deck → ai_id=-1 fallback (the documented "no AI assigned" sentinel
per AIBattleStartTask.cs:21). 3 new wire-shape tests assert the
camelCase keys land verbatim in the JSON, plus self/oppo info come from
the right sources.

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

SVSim.UnitTests/Controllers/RankBattleControllerTests.cs

@@ -66,6 +66,76 @@ public class RankBattleControllerTests
         Assert.That(j3.GetProperty("battle_id").GetString(), Is.EqualTo(j2.GetProperty("battle_id").GetString()));
     }
 
+    [Test]
+    public async Task AiStart_rotation_returns_ai_id_plus_self_oppo_info_camelCase_keys()
+    {
+        await using var factory = new SVSimTestFactory();
+        var viewerId = await factory.SeedViewerAsync(displayName: "TestViewer");
+        await factory.SeedGlobalsAsync();
+        await factory.SeedDeckAsync(viewerId, Format.Rotation, 1);
+        var client = factory.CreateAuthenticatedClient(viewerId);
+
+        var resp = await client.PostAsJsonAsync("/ai_rotation_rank_battle/start", new { });
+        var raw = await resp.Content.ReadAsStringAsync();
+
+        using var doc = JsonDocument.Parse(raw);
+        var data = doc.RootElement;
+        Assert.That(data.GetProperty("ai_id").GetInt32(), Is.InRange(4001, 4008));
+        Assert.That(data.GetProperty("turnState").GetInt32(), Is.EqualTo(0));
+
+        // Literal camelCase wire-key checks — these MUST be present verbatim
+        // (client uses JsonData.Keys.Contains).
+        Assert.That(raw, Does.Contain("\"userName\""), "Wire key must be camelCase, not snake_case.");
+        Assert.That(raw, Does.Contain("\"sleeveId\""));
+        Assert.That(raw, Does.Contain("\"emblemId\""));
+        Assert.That(raw, Does.Contain("\"degreeId\""));
+        Assert.That(raw, Does.Contain("\"fieldId\""));
+        Assert.That(raw, Does.Contain("\"isOfficial\""));
+        Assert.That(raw, Does.Contain("\"classId\""));
+        Assert.That(raw, Does.Contain("\"charaId\""));
+        Assert.That(raw, Does.Contain("\"isMasterRank\""));
+        Assert.That(raw, Does.Contain("\"battlePoint\""));
+        Assert.That(raw, Does.Contain("\"masterPoint\""));
+        // self_info / oppo_info / country_code stay snake_case (the outliers per ai-start.md).
+        Assert.That(raw, Does.Contain("\"self_info\""));
+        Assert.That(raw, Does.Contain("\"oppo_info\""));
+        Assert.That(raw, Does.Contain("\"country_code\""));
+    }
+
+    [Test]
+    public async Task AiStart_self_info_reflects_caller_user_name()
+    {
+        await using var factory = new SVSimTestFactory();
+        var viewerId = await factory.SeedViewerAsync(displayName: "Alice");
+        await factory.SeedGlobalsAsync();
+        await factory.SeedDeckAsync(viewerId, Format.Rotation, 1);
+        var client = factory.CreateAuthenticatedClient(viewerId);
+
+        var resp = await client.PostAsJsonAsync("/ai_rotation_rank_battle/start", new { });
+        using var doc = JsonDocument.Parse(await resp.Content.ReadAsStringAsync());
+        var selfInfo = doc.RootElement.GetProperty("self_info");
+
+        Assert.That(selfInfo.GetProperty("userName").GetString(), Is.EqualTo("Alice"));
+    }
+
+    [Test]
+    public async Task AiStart_oppo_info_reflects_roster_pick()
+    {
+        await using var factory = new SVSimTestFactory();
+        var viewerId = await factory.SeedViewerAsync(displayName: "PlayerA");
+        await factory.SeedGlobalsAsync();
+        await factory.SeedDeckAsync(viewerId, Format.Rotation, 1);
+        var client = factory.CreateAuthenticatedClient(viewerId);
+
+        var resp = await client.PostAsJsonAsync("/ai_rotation_rank_battle/start", new { });
+        using var doc = JsonDocument.Parse(await resp.Content.ReadAsStringAsync());
+        var oppoInfo = doc.RootElement.GetProperty("oppo_info");
+
+        // BotRoster's stub names contain "AI" — verify the roster was consulted.
+        Assert.That(oppoInfo.GetProperty("userName").GetString(), Does.Contain("AI"));
+        Assert.That(oppoInfo.GetProperty("classId").GetInt32(), Is.InRange(1, 8));
+    }
+
     [Test]
     public async Task Finish_emits_stubbed_zeros_with_battle_result_echo()
     {