feat(inventory): write acquire history rows on commit

CommitAsync now calls WriteAcquireHistory() between the two SaveChanges
calls: iterates _ops, skips SpendOps, writes one ViewerAcquireHistoryEntry
per GrantOp. Cascade rows get GrantSource.CardCosmeticCascade; wallet
currencies zero RewardDetailId; all rows in a single commit share one
DateTime.UtcNow timestamp. Closes _source plumbing from Task 5.

5 new tests added (46 total inventory, 0 failures).

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

SVSim.Database/Services/Inventory/InventoryTransaction.cs

@@ -277,6 +277,10 @@ internal sealed class InventoryTransaction : IInventoryTransaction
         ThrowIfCommitted();
 
         await _db.SaveChangesAsync(ct);
+
+        WriteAcquireHistory();
+        await _db.SaveChangesAsync(ct);
+
         await _dbTx.CommitAsync(ct);
         _committed = true;
 
@@ -285,6 +289,39 @@ internal sealed class InventoryTransaction : IInventoryTransaction
         return new InventoryCommitResult(rewardList, deltas);
     }
 
+    private void WriteAcquireHistory()
+    {
+        var now = DateTime.UtcNow;
+        var primaryMessage = GrantSourceMessages.For(_source);
+        var cascadeMessage = GrantSourceMessages.For(GrantSource.CardCosmeticCascade);
+
+        foreach (var op in _ops)
+        {
+            if (op is not GrantOp grant) continue;
+
+            var rowSource = grant.IsCascade ? GrantSource.CardCosmeticCascade : _source;
+            var rowMessage = grant.IsCascade ? cascadeMessage : primaryMessage;
+            var detailId = IsWalletCurrency(grant.Type) ? 0L : grant.DetailId;
+
+            _db.ViewerAcquireHistory.Add(new ViewerAcquireHistoryEntry
+            {
+                ViewerId = Viewer.Id,
+                RewardType = (int)grant.Type,
+                RewardDetailId = detailId,
+                RewardCount = grant.Num,
+                AcquireType = (int)rowSource,
+                Message = rowMessage,
+                AcquireTime = now,
+            });
+        }
+    }
+
+    private static bool IsWalletCurrency(UserGoodsType type) => type
+        is UserGoodsType.Crystal
+        or UserGoodsType.Rupy
+        or UserGoodsType.RedEther
+        or UserGoodsType.SpotCardPoint;
+
     private IReadOnlyList<GrantedReward> BuildRewardList()
     {
         // Pass 1 — for each currency type, find the last op (spend OR grant) that touched it