Store: show cached theme previews in grid and details panel

app/gui.py

@@ -1510,7 +1510,7 @@ class StoreDetailsPanel(QWidget):
         if lc is not None:
             rid, system = lc
         else:
-            rid, system = covers.stable_key(item["name"]), "games"
+            rid, system = covers.stable_key(item["name"]), item.get("system") or "games"
         self._set_cover(rid, system)
 
     def _set_cover(self, rid, system):
@@ -2033,7 +2033,12 @@ class StorePage(QWidget):
         else:
             rid, system = covers.stable_key(it["name"]), it.get("system") or "games"
         if not covers.is_scrapable(system):
-            return  # themes/DLC have no covers
+            # Themes/DLC aren't scraped, but a downloaded theme's preview is
+            # cached locally — show it when available.
+            p = covers.cover_path(rid, system)
+            if p.exists() and covers.file_is_image(p):
+                item.setIcon(QIcon(_fit_pixmap(QPixmap(str(p)), self.ICON_W, self.ICON_H)))
+            return
         p = covers.cover_path(rid, system)
         if p.exists() and covers.file_is_image(p):
             item.setIcon(QIcon(_fit_pixmap(QPixmap(str(p)), self.ICON_W, self.ICON_H)))