style: display total due, paid, and remaining balance in adherents list

as-talange-core/src/main/java/com/astalange/core/entity/Licence.java

@@ -83,6 +83,16 @@ public class Licence {
         return reste.compareTo(BigDecimal.ZERO) < 0 ? BigDecimal.ZERO : reste;
     }
 
+    @Transient
+    public BigDecimal getSommePayee() {
+        if (paiements == null || paiements.isEmpty()) {
+            return BigDecimal.ZERO;
+        }
+        return paiements.stream()
+                .map(Paiement::getMontant)
+                .reduce(BigDecimal.ZERO, BigDecimal::add);
+    }
+
     // Getters and Setters
 
     public Long getId() { return id; }