style(device_setup): redesign activation code dialog with icon and OK action

Replace the bare centered text with a rounded dialog that leads with a
mail icon, keeps the activation-code message, and adds an explicit OK
button to dismiss. Aligns the dialog with the rest of the legacy
design system.

modules/legacy/modules/legacy_auth/lib/src/features/device_setup/presentation/widgets/activation_code_dialog.dart

@@ -6,7 +6,9 @@ void showActivationCodeDialog(BuildContext context) {
   showDialog(
     context: context,
     builder: (context) => Dialog(
-      backgroundColor: Colors.transparent,
+      shape: RoundedRectangleBorder(
+        borderRadius: BorderRadius.circular(16),
+      ),
       child: _ActivationCodeDialog(),
     ),
   );
@@ -17,16 +19,46 @@ class _ActivationCodeDialog extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    return Container(
+    return Padding(
       padding: SizeUtils.getByScreen(
-        small: EdgeInsets.symmetric(horizontal: 14, vertical: 24),
-        big: EdgeInsets.symmetric(horizontal: 12, vertical: 20),
+        small: EdgeInsets.fromLTRB(24, 28, 24, 16),
+        big: EdgeInsets.fromLTRB(20, 24, 20, 14),
       ),
-      color: Colors.white,
-      child: Text(
-        context.translate(I18n.activationCodeMessage),
-        textAlign: TextAlign.center,
-        style: TextStyle(fontSize: SizeUtils.getByScreen(small: 16, big: 15)),
+      child: Column(
+        mainAxisSize: MainAxisSize.min,
+        children: [
+          Icon(
+            Icons.email_outlined,
+            size: SizeUtils.getByScreen(small: 48, big: 44),
+            color: const Color(0xFF329E95),
+          ),
+          SizedBox(height: SizeUtils.getByScreen(small: 16, big: 14)),
+          Text(
+            context.translate(I18n.activationCodeMessage),
+            textAlign: TextAlign.center,
+            style: TextStyle(
+              fontSize: SizeUtils.getByScreen(small: 15, big: 14),
+              height: 1.4,
+            ),
+          ),
+          SizedBox(height: SizeUtils.getByScreen(small: 20, big: 16)),
+          SizedBox(
+            width: double.infinity,
+            child: TextButton(
+              onPressed: () => Navigator.pop(context),
+              style: TextButton.styleFrom(
+                foregroundColor: const Color(0xFF329E95),
+              ),
+              child: Text(
+                context.translate(I18n.ok),
+                style: TextStyle(
+                  fontSize: SizeUtils.getByScreen(small: 15, big: 14),
+                  fontWeight: FontWeight.w600,
+                ),
+              ),
+            ),
+          ),
+        ],
       ),
     );
   }