feat(tk2): weighted-group reward picking

Replaces the all-rows-granted reward model with per-group weighted
pick. Each ArenaTwoPickReward row now belongs to a RewardGroup with a
Weight; finish/retire groups the WinCount's rows by RewardGroup and
picks exactly one row per group, weighted by Weight (excluding
Weight==0). A RewardNum==0 outcome skips both the grant and the
rewards[] emission. Empty WinCount catalogs emit empty arrays.

Existing seed entries preserve deterministic behavior by living in
single-option groups (each with weight 1). Future seasons can expand
groups to multi-option for true randomized rewards (e.g. 200-280
rupies).

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

SVSim.UnitTests/Importers/ArenaTwoPickRewardImporterTests.cs

@@ -38,6 +38,11 @@ public class ArenaTwoPickRewardImporterTests
         var w5 = rows.Where(r => r.WinCount == 5).ToList();
         Assert.That(w5.Single(r => r.RewardType == 4).RewardNum, Is.EqualTo(1));
         Assert.That(w5.Single(r => r.RewardType == 9).RewardNum, Is.EqualTo(1000));
+
+        // New columns: all rows should have weight=1 and win5 should span 2 distinct groups.
+        Assert.That(w5.All(r => r.Weight == 1), "all win5 rows should have Weight=1");
+        Assert.That(w5.Select(r => r.RewardGroup).Distinct().Count(), Is.EqualTo(2),
+            "win5 rewards split across 2 distinct groups (ticket + rupy)");
     }
 
     [Test]