add csfloat api usage

BlueLaminate/BlueLaminate.EFCore/Entities/Skin.cs

@@ -9,6 +9,19 @@ public class Skin
     /// <summary>Stable id from the CSGO-API catalogue, e.g. "skin-e757fd7191f9". The natural key.</summary>
     public string Slug { get; set; } = null!;
 
+    // CSFloat/CS item indexes, sourced from the static catalogue (weapon.weapon_id
+    // and paint_index). Together they identify a skin on CSFloat and let market
+    // listings join back to this catalogue row. Nullable until a sync populates
+    // them, since older catalogue rows predate these columns.
+    public int? DefIndex { get; set; }
+    public int? PaintIndex { get; set; }
+
+    // When the catalogue-driven listing sweep last fully covered this skin. The
+    // sweep processes least-recently-swept skins first (nulls = never swept), so
+    // capped runs chain across the whole catalogue and the stalest data refreshes
+    // first. Null until the first sweep reaches this skin.
+    public DateTimeOffset? ListingsSweptAt { get; set; }
+
     public string Name { get; set; } = null!;
     public string Rarity { get; set; } = null!;
     public string? Description { get; set; }