Improve form validation and guide users to fill out all the required fields

Updates form validation logic to allow zero quantity and adds quantity placeholder.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 91318273-c764-4fd4-be04-bdc12c38af32
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/0715008c-7244-40f4-befc-26c014852236/36c2c7b9-873e-432e-9d49-6ced2f07df49.jpg

client/src/components/NewSaleForm.tsx

@@ -281,7 +281,7 @@ export default function NewSaleForm({ onSaveSale }: NewSaleFormProps) {
                       <FormItem>
                         <FormLabel>Quantité <span className="text-destructive">*</span></FormLabel>
                         <FormControl>
-                          <Input type="number" min="1" placeholder="1" {...field} />
+                          <Input type="number" min="1" placeholder="Entrez la quantité" {...field} />
                         </FormControl>
                         <FormMessage />
                       </FormItem>

client/src/lib/validation.ts

@@ -30,7 +30,15 @@ export function validateRequiredFields(formData: any): string[] {
   ];
   
   return requiredFields
-    .filter(field => !formData[field.key] || formData[field.key].toString().trim() === '')
+    .filter(field => {
+      const value = formData[field.key];
+      // Pour la quantité, accepter 0 comme valeur valide
+      if (field.key === 'quantite') {
+        return value === '' || value === null || value === undefined;
+      }
+      // Pour les autres champs, vérifier si vide ou juste des espaces
+      return !value || value.toString().trim() === '';
+    })
     .map(field => field.label);
 }