Improve payment schedule tracking and sales analysis interface

Refactor Select component to handle undefined values and add a refresh button to the sales analysis iframe for forced reloads.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: 1e4433b5-47ab-464c-b663-fea2e53367dd
Replit-Commit-Checkpoint-Type: full_checkpoint
Replit-Commit-Event-Id: 18c68954-ece1-4351-bf35-d006a1a9307f
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/1957c339-2757-4d1f-8e92-e9f71a1ce58e/1e4433b5-47ab-464c-b663-fea2e53367dd/9uIte90

client/src/pages/Suppliers.tsx

@@ -531,14 +531,13 @@ export default function Suppliers() {
             <div>
               <Label htmlFor="paymentMethod">Mode de paiement</Label>
               <Select
-                value={formData.paymentMethod}
+                value={formData.paymentMethod || undefined}
                 onValueChange={(value) => handleChange('paymentMethod', value)}
               >
                 <SelectTrigger id="paymentMethod" data-testid="select-payment-method">
                   <SelectValue placeholder="Sélectionner un mode de paiement" />
                 </SelectTrigger>
                 <SelectContent>
-                  <SelectItem value="">Aucun</SelectItem>
                   <SelectItem value="Virement">Virement</SelectItem>
                   <SelectItem value="Traite">Traite</SelectItem>
                   <SelectItem value="Traite Magnétique">Traite Magnétique</SelectItem>