V2.5.1 — Dialogue licence custom + fix recadrage + style

- Dialogue de licence custom (remplace QInputDialog moche)
  - Logo CopyDev, champ stylise, bouton Activer cyan
  - Messages erreur/succes en dialogues custom colores
- Fix recadrage : reference au dialogue preservee avant destruction
- Splash screen sans bordure carree
- Style coherent gris/cyan sur tous les dialogues

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/splash.py

@@ -13,7 +13,12 @@ class SplashScreen(QWidget):
         self.setWindowFlags(Qt.WindowType.FramelessWindowHint | Qt.WindowType.WindowStaysOnTopHint)
         self.setAttribute(Qt.WidgetAttribute.WA_TranslucentBackground, False)
         self.setFixedSize(500, 400)
-        self.setStyleSheet("background-color: #f5f5f5; border: 1px solid #d0d0d0;")
+        self.setStyleSheet("""
+            QWidget {
+                background-color: #f5f5f5;
+                border-radius: 16px;
+            }
+        """)
 
         layout = QVBoxLayout(self)
         layout.setContentsMargins(40, 30, 40, 30)