feat(#152/#155): cleanup est_multiple + dashboard sans préfixe Admin (squash develop).

Suppression complète grossesse multiple / est_multiple (BDD, API, front).
Rename option C : widgets partagés et panels staff sous widgets/dashboard/,
AdminManagementWidget seul restant dans widgets/admin/.

frontend/lib/widgets/dashboard/validation_modal_theme.dart

@@ -0,0 +1,18 @@
+import 'package:flutter/material.dart';
+
+/// Couleurs / styles communs aux modales de validation (cohérent avec le violet / lavande admin).
+abstract final class ValidationModalTheme {
+  /// Violet pastel foncé (proche des cartes admin, ex. `0xFF6D4EA1`).
+  static const Color primaryActionBackground = Color(0xFF6D4EA1);
+  static const Color primaryActionForeground = Colors.white;
+
+  static ButtonStyle get primaryElevatedStyle {
+    return ElevatedButton.styleFrom(
+      backgroundColor: primaryActionBackground,
+      foregroundColor: primaryActionForeground,
+      disabledBackgroundColor: primaryActionBackground.withOpacity(0.45),
+      disabledForegroundColor: primaryActionForeground.withOpacity(0.7),
+    );
+  }
+}
+