feat(frontend): add ENSUP brand corners to home screen

eme-frontend/lib/screens/home_screen.dart

@@ -4,6 +4,7 @@ import "../theme/ensup_colors.dart";
 import "../widgets/ensup_top_bar.dart";
 import "../widgets/profile_card.dart";
 import "../widgets/action_card.dart";
+import "../widgets/brand_corners.dart";
 
 /// Écran d'accueil étudiant : profil + choix Emprunter / Restituer.
 class HomeScreen extends StatelessWidget {
@@ -19,7 +20,9 @@ class HomeScreen extends StatelessWidget {
   Widget build(BuildContext context) {
     return Scaffold(
       backgroundColor: EnsupColors.soft,
-      body: Center(
+      body: Stack(
+        children: [
+          Center(
             child: ConstrainedBox(
               constraints: const BoxConstraints(maxWidth: 1280, maxHeight: 820),
               child: Container(
@@ -83,7 +86,8 @@ class HomeScreen extends StatelessWidget {
                                     child: ActionCard(
                                       icon: Icons.assignment_return_outlined,
                                       title: "RESTITUER",
-                                  description: "Restituer un matériel que vous avez emprunté",
+                                      description:
+                                          "Restituer un matériel que vous avez emprunté",
                                       color: EnsupColors.teal,
                                       onTap: () => _bientot(context, "Restituer"),
                                     ),
@@ -100,6 +104,9 @@ class HomeScreen extends StatelessWidget {
               ),
             ),
           ),
+          const Positioned.fill(child: BrandCorners()),
+        ],
+      ),
     );
   }
 }

eme-frontend/lib/widgets/brand_corners.dart

@@ -0,0 +1,66 @@
+import "package:flutter/material.dart";
+import "../theme/ensup_colors.dart";
+
+/// Coins décoratifs de la charte ENSUP : un L coloré en haut-gauche et en
+/// bas-droit, en surimpression et non cliquables (comme dans la maquette).
+class BrandCorners extends StatelessWidget {
+  const BrandCorners({super.key});
+
+  @override
+  Widget build(BuildContext context) {
+    return IgnorePointer(
+      child: Stack(
+        children: [
+          Positioned(
+            top: 0,
+            left: 0,
+            child: CustomPaint(size: const Size(120, 120), painter: _TopLeftCornerPainter()),
+          ),
+          Positioned(
+            bottom: 0,
+            right: 0,
+            child: CustomPaint(size: const Size(120, 120), painter: _BottomRightCornerPainter()),
+          ),
+        ],
+      ),
+    );
+  }
+}
+
+const double _thickness = 22;
+
+class _TopLeftCornerPainter extends CustomPainter {
+  @override
+  void paint(Canvas canvas, Size size) {
+    final paint = Paint()..color = EnsupColors.red;
+    // Barre verticale gauche (rouge) + segment haut rouge.
+    canvas.drawRect(Rect.fromLTWH(0, 0, _thickness, size.height), paint);
+    canvas.drawRect(const Rect.fromLTWH(0, 0, 28, _thickness), paint);
+    // Segments colorés de la barre horizontale.
+    paint.color = EnsupColors.purple;
+    canvas.drawRect(const Rect.fromLTWH(28, 0, 22, _thickness), paint);
+    paint.color = EnsupColors.teal;
+    canvas.drawRect(const Rect.fromLTWH(50, 0, 22, _thickness), paint);
+  }
+
+  @override
+  bool shouldRepaint(covariant CustomPainter oldDelegate) => false;
+}
+
+class _BottomRightCornerPainter extends CustomPainter {
+  @override
+  void paint(Canvas canvas, Size size) {
+    final paint = Paint()..color = EnsupColors.cyan;
+    // Barre verticale droite (cyan) + segment bas cyan.
+    canvas.drawRect(Rect.fromLTWH(size.width - _thickness, 0, _thickness, size.height), paint);
+    canvas.drawRect(Rect.fromLTWH(size.width - 28, size.height - _thickness, 28, _thickness), paint);
+    // Segments colorés de la barre horizontale.
+    paint.color = EnsupColors.blue2;
+    canvas.drawRect(Rect.fromLTWH(size.width - 50, size.height - _thickness, 22, _thickness), paint);
+    paint.color = EnsupColors.blue3;
+    canvas.drawRect(Rect.fromLTWH(size.width - 72, size.height - _thickness, 22, _thickness), paint);
+  }
+
+  @override
+  bool shouldRepaint(covariant CustomPainter oldDelegate) => false;
+}