feat(theme): add appearance settings and theme provider integration

- Added theme selection in settings page for light, dark, and system modes.
- Integrated ThemeProvider into application layout.
- Updated dashboard layout to include theme toggle in the header.

frontend/src/app/(dashboard)/layout.tsx

@@ -8,6 +8,7 @@ import {
 	SidebarTrigger,
 } from "@/components/ui/sidebar";
 import { UserNavMobile } from "@/components/user-nav-mobile";
+import { ModeToggle } from "@/components/mode-toggle";
 
 export default function DashboardLayout({
 	children,
@@ -27,7 +28,10 @@ export default function DashboardLayout({
 							<div className="flex-1 flex justify-center">
 								<span className="font-bold text-primary text-lg">MemeGoat</span>
 							</div>
-							<UserNavMobile />
+							<div className="flex items-center gap-2">
+								<ModeToggle />
+								<UserNavMobile />
+							</div>
 						</header>
 						<main className="flex-1 overflow-y-auto bg-zinc-50 dark:bg-zinc-950">
 							{children}

frontend/src/app/(dashboard)/settings/page.tsx

@@ -1,7 +1,8 @@
 "use client";
 
 import { zodResolver } from "@hookform/resolvers/zod";
-import { Loader2, Save, User as UserIcon } from "lucide-react";
+import { Loader2, Moon, Laptop, Palette, Save, Sun, User as UserIcon } from "lucide-react";
+import { useTheme } from "next-themes";
 import * as React from "react";
 import { useForm } from "react-hook-form";
 import { toast } from "sonner";
@@ -24,6 +25,8 @@ import {
 	FormMessage,
 } from "@/components/ui/form";
 import { Input } from "@/components/ui/input";
+import { Label } from "@/components/ui/label";
+import { RadioGroup, RadioGroupItem } from "@/components/ui/radio-group";
 import { Spinner } from "@/components/ui/spinner";
 import { Textarea } from "@/components/ui/textarea";
 import { useAuth } from "@/providers/auth-provider";
@@ -37,8 +40,14 @@ const settingsSchema = z.object({
 type SettingsFormValues = z.infer<typeof settingsSchema>;
 
 export default function SettingsPage() {
+	const { theme, setTheme } = useTheme();
 	const { user, isLoading, refreshUser } = useAuth();
 	const [isSaving, setIsSaving] = React.useState(false);
+	const [mounted, setMounted] = React.useState(false);
+
+	React.useEffect(() => {
+		setMounted(true);
+	}, []);
 
 	const form = useForm<SettingsFormValues>({
 		resolver: zodResolver(settingsSchema),
@@ -185,6 +194,55 @@ export default function SettingsPage() {
 					</Form>
 				</CardContent>
 			</Card>
+<Card className="mt-8">
+				<CardHeader>
+					<div className="flex items-center gap-2">
+						<Palette className="h-5 w-5 text-primary" />
+						<CardTitle>Apparence</CardTitle>
+					</div>
+					<CardDescription>
+						Personnalisez l'apparence de l'application selon vos préférences.
+					</CardDescription>
+				</CardHeader>
+				<CardContent>
+					<RadioGroup
+						value={mounted ? theme : "system"}
+						onValueChange={(value) => setTheme(value)}
+						className="grid grid-cols-1 sm:grid-cols-3 gap-4"
+					>
+						<div>
+							<RadioGroupItem value="light" id="light" className="peer sr-only" />
+							<Label
+								htmlFor="light"
+								className="flex flex-col items-center justify-between rounded-md border-2 border-muted bg-popover p-4 hover:bg-accent hover:text-accent-foreground peer-data-[state=checked]:border-primary [&:has([data-state=checked])]:border-primary cursor-pointer"
+							>
+								<Sun className="mb-3 h-6 w-6" />
+								<span>Clair</span>
+							</Label>
+						</div>
+						<div>
+							<RadioGroupItem value="dark" id="dark" className="peer sr-only" />
+							<Label
+								htmlFor="dark"
+								className="flex flex-col items-center justify-between rounded-md border-2 border-muted bg-popover p-4 hover:bg-accent hover:text-accent-foreground peer-data-[state=checked]:border-primary [&:has([data-state=checked])]:border-primary cursor-pointer"
+							>
+								<Moon className="mb-3 h-6 w-6" />
+								<span>Sombre</span>
+							</Label>
+						</div>
+						<div>
+							<RadioGroupItem value="system" id="system" className="peer sr-only" />
+							<Label
+								htmlFor="system"
+								className="flex flex-col items-center justify-between rounded-md border-2 border-muted bg-popover p-4 hover:bg-accent hover:text-accent-foreground peer-data-[state=checked]:border-primary [&:has([data-state=checked])]:border-primary cursor-pointer"
+							>
+								<Laptop className="mb-3 h-6 w-6" />
+								<span>Système</span>
+							</Label>
+						</div>
+					</RadioGroup>
+				</CardContent>
+			</Card>
 		</div>
 	);
 }

frontend/src/app/layout.tsx

@@ -2,6 +2,7 @@ import type { Metadata } from "next";
 import { Ubuntu_Mono, Ubuntu_Sans } from "next/font/google";
 import { Toaster } from "@/components/ui/sonner";
 import { AuthProvider } from "@/providers/auth-provider";
+import { ThemeProvider } from "@/providers/theme-provider";
 import "./globals.css";
 
 const ubuntuSans = Ubuntu_Sans({
@@ -60,10 +61,17 @@ export default function RootLayout({
 			<body
 				className={`${ubuntuSans.variable} ${ubuntuMono.variable} antialiased`}
 			>
-				<AuthProvider>
-					{children}
-					<Toaster />
-				</AuthProvider>
+				<ThemeProvider
+					attribute="class"
+					defaultTheme="system"
+					enableSystem
+					disableTransitionOnChange
+				>
+					<AuthProvider>
+						{children}
+						<Toaster />
+					</AuthProvider>
+				</ThemeProvider>
 			</body>
 		</html>
 	);