Clean up enrollment screen (#234)

## Android

Blank form:
|Before|After|
|--|--|
|<img width="395" alt="image" src="https://github.com/user-attachments/assets/5c8a8e26-d030-4b14-b91a-9cbf5e1b2e50" />|<img width="393" alt="Android Studio 2025-01-24 11 34 32" src="https://github.com/user-attachments/assets/408c8003-9bc0-4e09-af58-44f5728dcb59" />|

Text entered:
|Before|After|
|--|--|
|<img width="397" alt="Arc 2025-01-24 11 47 19" src="https://github.com/user-attachments/assets/d5e8bc70-1786-488c-aa1c-c45ddf9a92de" />|<img width="393" alt="image" src="https://github.com/user-attachments/assets/5765e9c3-cf50-4913-b4d1-78780918f35d" />|

Submitted empty:
|Before|After|
|--|--|
|<img width="395" alt="image" src="https://github.com/user-attachments/assets/37b8b9c8-760f-479e-b39f-3502367567ec" />|<img width="397" alt="Android Studio 2025-01-24 11 34 47" src="https://github.com/user-attachments/assets/c381725e-f449-43de-961f-768205b60028" />|

Submitted invalid:
|Before|After|
|--|--|
|<img width="388" alt="image" src="https://github.com/user-attachments/assets/3a3859e1-eff7-4111-9dd0-15edbd3bb998" />|<img width="389" alt="image" src="https://github.com/user-attachments/assets/1ab811df-e3ff-4a1f-9d3d-a2869cbc1877" />|


Unchanged:
<img width="388" alt="image" src="https://github.com/user-attachments/assets/f2719677-a73f-435d-b3c6-a0a4fd64759b" />


## iOS


Blank form:
|Before|After|
|--|--|
|<img width="454" alt="image" src="https://github.com/user-attachments/assets/9afed9d1-c63b-4fcf-80a8-c2a9d2c18e76" />|<img width="454" alt="image" src="https://github.com/user-attachments/assets/c185b7f1-a2b3-4e9b-a49f-fb9790214c3a" />|

Text entered:
|Before|After|
|--|--|
|<img width="452" alt="image" src="https://github.com/user-attachments/assets/d3be265d-9076-4a19-865b-413dfad79ed4" />|<img width="466" alt="image" src="https://github.com/user-attachments/assets/c23e99eb-1001-4f80-b88f-62ffa8c8f7dd" />|


Submitted empty:
(note it says invalid before)
|Before|After|
|--|--|
|<img width="463" alt="image" src="https://github.com/user-attachments/assets/e26c0642-e6cc-4e97-885d-b0309e58ace6" />|<img width="455" alt="image" src="https://github.com/user-attachments/assets/95b8f975-41b5-48a0-b75a-9cb6a9acc50e" />|

Submitted invalid:
|Before|After|
|--|--|
|<img width="484" alt="image" src="https://github.com/user-attachments/assets/1daf3c2e-5fbb-477c-b0c7-66689170d97a" />|<img width="463" alt="image" src="https://github.com/user-attachments/assets/8bef248f-a607-4373-9e9e-6ff08f402b4a" />|

lib/screens/EnrollmentScreen.dart

@@ -1,4 +1,5 @@
 import 'dart:async';
+import 'dart:io';
 
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
@@ -6,8 +7,12 @@ import 'package:flutter/services.dart';
 import 'package:flutter_platform_widgets/flutter_platform_widgets.dart';
 
 import 'package:mobile_nebula/components/SimplePage.dart';
+import 'package:mobile_nebula/components/buttons/PrimaryButton.dart';
 import 'package:url_launcher/url_launcher.dart';
 
+import '../components/config/ConfigItem.dart';
+import '../components/config/ConfigSection.dart';
+
 class EnrollmentScreen extends StatefulWidget {
   final String? code;
   final StreamController? stream;
@@ -105,7 +110,7 @@ class _EnrollmentScreenState extends State<EnrollmentScreen> {
           Padding(
               child: SelectableText(
                   'There was an issue while attempting to enroll this device. Contact your administrator to obtain a new enrollment code.'),
-              padding: EdgeInsets.symmetric(vertical: 20)),
+              padding: EdgeInsets.symmetric(horizontal: 16, vertical: 20)),
           Padding(
               child: SelectableText.rich(TextSpan(children: [
                 TextSpan(text: 'If the problem persists, please let us know at '),
@@ -121,9 +126,9 @@ class _EnrollmentScreenState extends State<EnrollmentScreen> {
                 ),
                 TextSpan(text: ' and provide the following error:'),
               ])),
-              padding: EdgeInsets.only(bottom: 10)),
+              padding: EdgeInsets.symmetric(horizontal: 16, vertical: 10)),
           Container(
-            child: Padding(child: SelectableText(this.error!), padding: EdgeInsets.all(10)),
+            child: Padding(child: SelectableText(this.error!), padding: EdgeInsets.all(16)),
             color: Theme.of(context).colorScheme.errorContainer,
           ),
         ],
@@ -151,30 +156,59 @@ class _EnrollmentScreenState extends State<EnrollmentScreen> {
       ]));
     }
 
-    return SimplePage(
+    return SimplePage(title: Text('Enroll with Managed Nebula'), child: child, alignment: alignment);
-        title: Text('Enroll with Managed Nebula', style: TextStyle(fontWeight: FontWeight.bold)),
-        child: Padding(child: child, padding: EdgeInsets.symmetric(horizontal: 10)),
-        alignment: alignment);
   }
 
   Widget _codeEntry() {
+    final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
+
+    String? validator(String? value) {
+      if (value == null || value.isEmpty) {
+        return 'Code or link is required';
+      }
+      return null;
+    }
+
+    Future<void> onSubmit() async {
+      final bool isValid = _formKey.currentState?.validate() ?? false;
+      if (!isValid) {
+        return;
+      }
+
+      setState(() {
+        code = EnrollmentScreen.parseCode(enrollInput.text);
+        error = null;
+        _enroll();
+      });
+    }
+
+    final input = Padding(
+        padding: EdgeInsets.symmetric(horizontal: 16),
+        child: PlatformTextFormField(
+          controller: enrollInput,
+          validator: validator,
+          hintText: 'from admin.defined.net',
+          cupertino: (_, __) => CupertinoTextFormFieldData(
+            prefix: Text("Code or link"),
+          ),
+          material: (_, __) => MaterialTextFormFieldData(
+            decoration: const InputDecoration(labelText: 'Code or link'),
+          ),
+        ));
+
+    final form = Form(
+      key: _formKey,
+      child: Platform.isAndroid ? input : ConfigSection(children: [input]),
+    );
+
     return Column(children: [
       Padding(
-          padding: EdgeInsets.only(top: 20),
+        padding: EdgeInsets.symmetric(vertical: 32),
-          child: PlatformTextField(
+        child: form,
-            hintText: 'defined.net enrollment code or link',
+      ),
-            controller: enrollInput,
+      Padding(
-          )),
+          padding: EdgeInsets.symmetric(horizontal: 16),
-      PlatformTextButton(
+          child: Row(children: [Expanded(child: PrimaryButton(child: Text('Submit'), onPressed: onSubmit))]))
-        child: Text('Submit'),
-        onPressed: () {
-          setState(() {
-            code = EnrollmentScreen.parseCode(enrollInput.text);
-            error = null;
-            _enroll();
-          });
-        },
-      )
     ]);
   }
 }