fix(auth): 登录注册与手机号登录键盘避让

lib/core/platform/keyboard_inset.dart

@@ -1,8 +1,29 @@
 // Author: fruit.com.cn
 
+import 'dart:math' as math;
+
 import 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
 import 'package:flutter/services.dart';
 
+/// iOS 使用实时 viewInsets；Android adjustNothing 下取 MethodChannel 最大值。
+double effectiveKeyboardInset(
+  BuildContext context,
+  KeyboardInsetNotifier notifier, {
+  double maxRatio = 0.6,
+}) {
+  final media = MediaQuery.of(context);
+  final viewInset = media.viewInsets.bottom;
+  final channelInset =
+      !kIsWeb && defaultTargetPlatform == TargetPlatform.android
+      ? notifier.value / media.devicePixelRatio
+      : 0.0;
+  final inset = math.max(viewInset, channelInset);
+  final maxInset = media.size.height * maxRatio;
+  if (!inset.isFinite || inset > maxInset) return 0;
+  return math.max(0, inset);
+}
+
 /// Provides the Android IME height even when `adjustNothing` keeps
 /// `MediaQuery.viewInsets` at zero.
 class KeyboardInsetNotifier extends ChangeNotifier {