docs(inventory): explain two-phase prune query (SQLite constraint)

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

SVSim.Database/Services/Inventory/InventoryTransaction.cs

@@ -296,6 +296,7 @@ internal sealed class InventoryTransaction : IInventoryTransaction
 
     private async Task PruneAcquireHistoryAsync(CancellationToken ct)
     {
+        // Two-phase: SQLite (used in tests) cannot translate Skip+OrderBy inside ExecuteDeleteAsync.
         var overflowIds = await _db.ViewerAcquireHistory
             .Where(h => h.ViewerId == Viewer.Id)
             .OrderByDescending(h => h.AcquireTime).ThenByDescending(h => h.Id)