feat: implement shared LoadingModal component and integrate into dashboard route loading states

src/app/(dashboard)/grid/loading.tsx

@@ -1,39 +1,5 @@
-export default function GridLoading() {
-    return (
-        <div className="fixed inset-0 z-50 flex items-center justify-center bg-black/40 backdrop-blur-sm">
-            <div
-                className="flex flex-col items-center gap-5 px-10 py-8 rounded-2xl shadow-2xl border"
-                style={{
-                    background: "var(--bg-elevated)",
-                    borderColor: "var(--border)",
-                }}
-            >
-                {/* Spinner */}
-                <div className="relative w-12 h-12">
-                    <div
-                        className="absolute inset-0 rounded-full border-[3px] animate-spin"
-                        style={{
-                            borderColor: "var(--border)",
-                            borderTopColor: "var(--accent)",
-                        }}
-                    />
-                </div>
+import LoadingModal from "@/components/shared/loading-modal";
 
-                <div className="flex flex-col items-center gap-1.5">
-                    <span
-                        className="text-sm font-semibold tracking-wide"
-                        style={{ color: "var(--text-primary)" }}
-                    >
-                        Chargement des données
-                    </span>
-                    <span
-                        className="text-xs"
-                        style={{ color: "var(--text-muted)" }}
-                    >
-                        Récupération des articles et calcul des scores...
-                    </span>
-                </div>
-            </div>
-        </div>
-    );
+export default function GridLoading() {
+    return <LoadingModal message="Chargement des données" subMessage="Récupération des articles et calcul des scores..." />;
 }