chore: suppression artefacts Xmass — portraits PNG, WildCoin, entries formation

- Suppression dossier png/ (13 fichiers portraits formation + w-coin + bg-cover legacy)
- Suppression entries Achievements 48-58 (portraits promo Wild Code School)
- Remplacement icône monnaie w-coin.png → tadpole.svg dans boutiquecard

Frontend/src/scss/components/boutiquecard.scss

@@ -56,7 +56,7 @@
         .priceicon {
           width: 22px;
           height: 22px;
-          background-image: url("/png/w-coin.png");
+          background-image: url("/svg/tadpole.svg");
           background-size: contain;
           background-position: center;
           background-repeat: no-repeat;