refactor: split registration page into focused parts

lib/pages/registration/parts/registration_status_part.dart

@@ -0,0 +1,55 @@
+// ignore_for_file: invalid_use_of_protected_member
+
+part of '../../registration_page.dart';
+
+extension _RegistrationStatusPart on _RegistrationPageState {
+  void _clearStatusOverride() {
+    _statusOverrideText = null;
+    _statusOverrideDot = null;
+  }
+
+  void _showStatusOverride(String text, StatusDotColor dot, Duration duration) {
+    setState(() {
+      _statusOverrideText = text;
+      _statusOverrideDot = dot;
+    });
+    Future.delayed(duration, () {
+      if (mounted) setState(() => _clearStatusOverride());
+    });
+  }
+
+  void _updateBaseStatus() {
+    if (_isSubmitting) {
+      _statusDot = StatusDotColor.orange;
+      _statusText = '正在提交…';
+      return;
+    }
+    if (_mode == RegistrationMode.multiCode &&
+        _locationCode != null &&
+        _zongpaiNos.isEmpty) {
+      _statusDot = StatusDotColor.blue;
+      _statusText = '多码上架模式，请扫描下一张执行卡';
+      return;
+    }
+    final hasZongpai = _zongpaiNos.isNotEmpty;
+    final hasLocation = _locationCode != null;
+    if (hasZongpai && hasLocation) {
+      _statusDot = StatusDotColor.blue;
+      _statusText = '请确认信息并提交';
+    } else if (hasZongpai) {
+      _statusDot = StatusDotColor.blue;
+      _statusText = '请扫描目标货位号';
+    } else if (hasLocation) {
+      _statusDot = StatusDotColor.blue;
+      _statusText = '请扫描执行卡';
+    } else {
+      _statusDot = StatusDotColor.blue;
+      _statusText = '等待扫描总排号或货位号…';
+    }
+  }
+
+  bool get _canSubmit =>
+      _zongpaiNos.isNotEmpty && _locationCode != null && !_isSubmitting;
+
+  bool get _isTransitTarget => isTransitTarget(_locationType, _locationCode);
+}