feat(config): wire /config/update + /config/update_challenge_config (closes family 4/4)

is_skip_gacha_effect, use_challenge_two_pick_premium_card, and
challenge_two_pick_sleeve_id all persist on ViewerInfo and round-trip
through /load/index.

The two challenge fields move from the global ChallengeConfig section to
ViewerInfo — they're viewer preferences, not server-wide policy. Premium
card defaults to 0; sleeve falls back to DefaultLoadoutConfig.SleeveId
(3000011) when unset. MatchContextBuilder's TK2 sleeve read switches to
the same viewer-scoped path.

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

SVSim.EmulatedEntrypoint/Models/Dtos/Requests/ConfigUpdateChallengeConfigRequest.cs

@@ -0,0 +1,16 @@
+using MessagePack;
+using System.Text.Json.Serialization;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Requests;
+
+[MessagePackObject]
+public class ConfigUpdateChallengeConfigRequest : BaseRequest
+{
+    [JsonPropertyName("use_challenge_two_pick_premium_card")]
+    [Key("use_challenge_two_pick_premium_card")]
+    public int UseChallengeTwoPickPremiumCard { get; set; }
+
+    [JsonPropertyName("challenge_two_pick_sleeve_id")]
+    [Key("challenge_two_pick_sleeve_id")]
+    public long ChallengeTwoPickSleeveId { get; set; }
+}

SVSim.EmulatedEntrypoint/Models/Dtos/Requests/ConfigUpdateRequest.cs

@@ -0,0 +1,12 @@
+using MessagePack;
+using System.Text.Json.Serialization;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.Requests;
+
+[MessagePackObject]
+public class ConfigUpdateRequest : BaseRequest
+{
+    [JsonPropertyName("is_skip_gacha_effect")]
+    [Key("is_skip_gacha_effect")]
+    public int IsSkipGachaEffect { get; set; }
+}

SVSim.EmulatedEntrypoint/Models/Dtos/UserConfig.cs

@@ -27,4 +27,7 @@ public class UserConfig
     [JsonPropertyName("is_prize_preferred")]
     [Key("is_prize_preferred")]
     public int IsPrizePreferred { get; set; }
+    [JsonPropertyName("is_skip_gacha_effect")]
+    [Key("is_skip_gacha_effect")]
+    public int IsSkipGachaEffect { get; set; }
 }