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

src/components/shared/loading-modal.tsx

@@ -0,0 +1,45 @@
+interface LoadingModalProps {
+    message?: string;
+    subMessage?: string;
+}
+
+export default function LoadingModal({
+    message = "Chargement des données",
+    subMessage = "Veuillez patienter...",
+}: LoadingModalProps) {
+    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)",
+                }}
+            >
+                <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>
+                <div className="flex flex-col items-center gap-1.5">
+                    <span
+                        className="text-sm font-semibold tracking-wide"
+                        style={{ color: "var(--text-primary)" }}
+                    >
+                        {message}
+                    </span>
+                    <span
+                        className="text-xs"
+                        style={{ color: "var(--text-muted)" }}
+                    >
+                        {subMessage}
+                    </span>
+                </div>
+            </div>
+        </div>
+    );
+}