feat(rewards): add 14 new shop items with twin backgrounds

Each page background gets a matching banner background. Tests verify
pairing, price constraints, and code length limits

readme.md

@@ -65,7 +65,7 @@ To Be Played is split into three repositories:
   snapshots, once per user, kind and game (`ref`). Rules and numbers: `RewardRules`; a Steam finish needs playtime and one
   proof of fresh play (ending achievement or playtime around the finish, or half of the IGDB time played since the finish; old history pays nothing). The month bonus needs a finished game in that month. Games added by hand pay 15 for
   a finish, at most 3 per ISO week. The settle takes a per-user advisory lock. V26 also pays a one-time starter grant
-  for finishes from before the status log. Shop: a whitelist of 43 looks (`ShopItem`; 31 buyable and 12 unlock-only) in eight slots, including animated completed effects, page backgrounds,
+  for finishes from before the status log. Shop: a whitelist of 57 looks (`ShopItem`; 45 buyable and 12 unlock-only) in eight slots, including animated completed effects, page backgrounds (CSS, SVG and two canvas engines in the Frontend),
   banner backgrounds (V27 widens `reward_equipped.slot`) and three buyable skins (full themes, slot `SKIN`). The unlock-only
   items (price 0, never sold): the settle books an `UNLOCK` row (ref = item code, 0 points) once a
   track reaches the item's target, retroactively and never lost. The five tracks (`Unlocks`): games finished