feat: implement NotificationHandler component for real-time notifications

- Added `NotificationHandler` component for managing real-time notifications using sockets.
- Display notifications for comments, replies, likes, and messages with interactive toasts.
- Integrated click handling for navigation to relevant pages based on notification type.

frontend/src/components/notification-handler.tsx

@@ -0,0 +1,116 @@
+"use client";
+
+import { Bell, Heart, MessageCircle, Reply } from "lucide-react";
+import { useRouter } from "next/navigation";
+import * as React from "react";
+import { toast } from "sonner";
+import { useSocket } from "@/providers/socket-provider";
+
+interface NotificationData {
+	type: "comment" | "reply" | "like_comment" | "message";
+	userId: string;
+	username: string;
+	contentId?: string;
+	commentId?: string;
+	text: string;
+}
+
+export function NotificationHandler() {
+	const { socket } = useSocket();
+	const router = useRouter();
+
+	React.useEffect(() => {
+		if (!socket) return;
+
+		const handleNotification = (data: NotificationData) => {
+			// Ne pas afficher de toast si on est déjà sur la page des messages pour un nouveau message
+			if (data.type === "message" && window.location.pathname === "/messages") {
+				return;
+			}
+
+			toast.custom(
+				(t) => (
+					<div
+						role="button"
+						tabIndex={0}
+						className="flex items-start gap-3 bg-white dark:bg-zinc-900 p-4 rounded-xl shadow-lg border border-zinc-200 dark:border-zinc-800 w-full max-w-sm cursor-pointer hover:bg-zinc-50 dark:hover:bg-zinc-800 transition-colors"
+						onClick={() => {
+							toast.dismiss(t);
+							if (data.type === "message") {
+								router.push("/messages");
+							} else if (data.contentId) {
+								router.push(`/meme/${data.contentId}`);
+							}
+						}}
+						onKeyDown={(e) => {
+							if (e.key === "Enter" || e.key === " ") {
+								toast.dismiss(t);
+								if (data.type === "message") {
+									router.push("/messages");
+								} else if (data.contentId) {
+									router.push(`/meme/${data.contentId}`);
+								}
+							}
+						}}
+					>
+						<div className="bg-primary/10 p-2 rounded-full shrink-0">
+							{data.type === "comment" && (
+								<MessageCircle className="h-4 w-4 text-primary" />
+							)}
+							{data.type === "reply" && <Reply className="h-4 w-4 text-primary" />}
+							{data.type === "like_comment" && (
+								<Heart className="h-4 w-4 text-red-500" />
+							)}
+							{data.type === "message" && (
+								<MessageCircle className="h-4 w-4 text-primary" />
+							)}
+						</div>
+						<div className="flex-1 overflow-hidden">
+							<p className="text-sm font-bold">@{data.username}</p>
+							<p className="text-xs text-muted-foreground truncate">{data.text}</p>
+						</div>
+						<button
+							type="button"
+							onClick={(e) => {
+								e.stopPropagation();
+								toast.dismiss(t);
+							}}
+							className="text-muted-foreground hover:text-foreground"
+						>
+							<Bell className="h-3 w-3" />
+						</button>
+					</div>
+				),
+				{
+					duration: 5000,
+					position: "top-right",
+				},
+			);
+		};
+
+		socket.on("notification", handleNotification);
+
+		// Aussi pour les nouveaux messages (si on veut un toast global)
+		socket.on("new_message", (data: { message: any }) => {
+			if (window.location.pathname !== "/messages") {
+				toast(
+					`Nouveau message de @${data.message.sender?.username || "un membre"}`,
+					{
+						description: data.message.text.substring(0, 50),
+						action: {
+							label: "Voir",
+							onClick: () => router.push("/messages"),
+						},
+					},
+				);
+			}
+		});
+
+		return () => {
+			socket.off("notification");
+			socket.off("new_message");
+		};
+	}, [socket, router]);
+
+	return null;
+}