redesigned payment page + a lot of fixes

frontend/pweb/lib/controllers/auth/email.dart

@@ -0,0 +1,44 @@
+import 'package:flutter/material.dart';
+
+import 'package:email_validator/email_validator.dart';
+
+
+class EmailFieldController {
+  final TextEditingController textController;
+  final ValueNotifier<bool> isValid;
+
+  EmailFieldController({
+    TextEditingController? controller,
+  })  : textController = controller ?? TextEditingController(),
+        isValid = ValueNotifier<bool>(false);
+
+  String get text => textController.text;
+
+  void setText(String value) {
+    textController.text = value;
+    onChanged(value);
+  }
+
+  bool _isValidEmail(String? value) {
+    final trimmed = value?.trim() ?? '';
+    if (trimmed.isEmpty) {
+      return false;
+    }
+    return EmailValidator.validate(trimmed);
+  }
+
+  String? validate(String? value, String invalidMessage) {
+    final result = _isValidEmail(value) ? null : invalidMessage;
+    isValid.value = result == null;
+    return result;
+  }
+
+  void onChanged(String? value) {
+    isValid.value = _isValidEmail(value);
+  }
+
+  void dispose() {
+    textController.dispose();
+    isValid.dispose();
+  }
+}