Allow negative amounts to be processed in credit notes

Update the credit note schema to accept all numeric values (positive, negative, zero) and handle null amounts by converting them to undefined.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 9fcf4b21-eb0c-4e53-a567-e2ce4a6ad869
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/1957c339-2757-4d1f-8e92-e9f71a1ce58e/9fcf4b21-eb0c-4e53-a567-e2ce4a6ad869/Ii96ETr

client/src/pages/Avoirs.tsx

@@ -80,6 +80,10 @@ const avoirSchema = z.object({
     z.null().transform(() => undefined),
     z.undefined().transform(() => undefined), 
     z.literal("").transform(() => undefined),
+    z.number().transform((num) => {
+      // Permettre tous les nombres existants (positifs, négatifs, zéro)
+      return num;
+    }),
     z.string().transform((val) => {
       if (val.trim() === '') return undefined; // Permettre les champs vides
       const num = parseFloat(val);
@@ -397,7 +401,7 @@ export default function Avoirs() {
       supplierId: avoir.supplierId || 0,
       groupId: avoir.groupId || 0,
       invoiceReference: avoir.invoiceReference || "",
-      amount: avoir.amount,
+      amount: avoir.amount ?? undefined, // ✅ Convertir null en undefined pour permettre la suppression
       comment: avoir.comment || "",
       commercialProcessed: avoir.commercialProcessed || false,
       status: avoir.status || "En attente de demande",