feat: Implement core grid state management with Zustand, define grid data types, and introduce a heatmap cell component.

src/features/grid/components/floating-summary-bar.tsx

@@ -145,6 +145,10 @@ export function FloatingSummaryBar() {
             </div>
 
             <div className="flex space-x-12 items-center">
+                <Stat
+                    label="Nombre de Produits"
+                    value={summary.totalProducts.toLocaleString("fr-FR")}
+                />
                 <Stat
                     label="Volume Total Vendu"
                     value={Math.round(summary.totalQuantite).toLocaleString("fr-FR")}

src/features/grid/components/heatmap-cell.tsx

@@ -15,7 +15,7 @@ function getHeatmapClass(value: number | null): string {
 
 export const HeatmapCell = React.memo(({ value }: HeatmapCellProps) => {
     const heatClass = getHeatmapClass(value);
-    const display = value === null || value === 0 ? "—" : Math.round(Math.abs(value)).toString();
+    const display = value === null || value === 0 ? "0" : Math.round(Math.abs(value)).toString();
 
     return (
         <div