refactor: extract boxing logic into dedicated modules with tests

- boxing_models.dart: add BoxingMode, BoxingPhase, BoxingPageArguments
- boxing_box_mutations.dart: box item add/replace/remove operations
- boxing_calculations.dart: pure calculation helpers (quantities, validation)
- boxing_status_presenter.dart: status bar text/dot determination
- dialogs/cross_paichan_dialog.dart: cross-paichan confirmation dialog
- widgets/boxing_notice_banners.dart: notice banner widgets
- Add unit tests for mutations, calculations, and status presenter

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

test/pages/boxing/boxing_status_presenter_test.dart

@@ -0,0 +1,81 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:pad_scanner/pages/boxing/boxing_models.dart';
+import 'package:pad_scanner/pages/boxing/boxing_status_presenter.dart';
+import 'package:pad_scanner/widgets/status_bar.dart';
+
+void main() {
+  BoxingStatusPresentation status({
+    bool isAutoProcessing = false,
+    bool isSubmitting = false,
+    bool isDuplicateBoxNo = false,
+    bool quantityTooHigh = false,
+    bool isEditingAssigned = false,
+    bool isDeletingAssigned = false,
+    bool hasPaichanSwitchNotice = false,
+    BoxingPhase phase = BoxingPhase.waiting,
+    bool isMultiCode = false,
+    bool hasVisibleManyToOneItems = false,
+    int remainingQuantity = 1,
+    String boxNoText = '1',
+  }) {
+    return boxingStatusFor(
+      isAutoProcessing: isAutoProcessing,
+      isSubmitting: isSubmitting,
+      isDuplicateBoxNo: isDuplicateBoxNo,
+      quantityTooHigh: quantityTooHigh,
+      isEditingAssigned: isEditingAssigned,
+      isDeletingAssigned: isDeletingAssigned,
+      hasPaichanSwitchNotice: hasPaichanSwitchNotice,
+      phase: phase,
+      isMultiCode: isMultiCode,
+      hasVisibleManyToOneItems: hasVisibleManyToOneItems,
+      remainingQuantity: remainingQuantity,
+      boxNoText: boxNoText,
+    );
+  }
+
+  group('boxingStatusFor', () {
+    test('reports waiting and multi-code continuation states', () {
+      expect(status().text, '等待扫码');
+      final multi = status(isMultiCode: true, hasVisibleManyToOneItems: true);
+      expect(multi.text, '请继续扫码或完成本箱');
+    });
+
+    test('prioritizes transient and validation states', () {
+      expect(status(isSubmitting: true).text, '正在提交…');
+      expect(
+        status(isDuplicateBoxNo: true, phase: BoxingPhase.scanned).dot,
+        StatusDotColor.amber,
+      );
+      expect(
+        status(quantityTooHigh: true, phase: BoxingPhase.scanned).text,
+        '超出可装数量上限',
+      );
+    });
+
+    test('reports edit delete and switched paichan states', () {
+      expect(status(isEditingAssigned: true).text, '正在编辑已分配记录');
+      expect(status(isDeletingAssigned: true).dot, StatusDotColor.red);
+      expect(status(hasPaichanSwitchNotice: true).text, '排产号已切换，箱号已重置');
+    });
+
+    test('reports scanned completed and submitted states', () {
+      expect(
+        status(phase: BoxingPhase.scanned, remainingQuantity: 0).text,
+        '该总排号已全部装箱完毕',
+      );
+      expect(
+        status(phase: BoxingPhase.scanned, remainingQuantity: 2).text,
+        '数量已填入，请确认或修改',
+      );
+      expect(
+        status(phase: BoxingPhase.submitted, isMultiCode: false).text,
+        '装箱成功，可继续扫码',
+      );
+      expect(
+        status(phase: BoxingPhase.submitted, isMultiCode: true).text,
+        '请扫描下一个总排号',
+      );
+    });
+  });
+}