feat(client): 购买模型/仓库切 pay v2 契约（render_type 多态 + 分金额 + 订单列表）

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

client/test/money_test.dart

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+import 'package:flutter_test/flutter_test.dart';
+import 'package:jiu_client/core/utils/money.dart';
+
+void main() {
+  group('yuanFromMinor()', () {
+    test('299900 分 → "2,999.00"（千分位 + 两位小数）', () {
+      expect(yuanFromMinor(299900), '2,999.00');
+    });
+
+    test('100 分 → "1.00"', () {
+      expect(yuanFromMinor(100), '1.00');
+    });
+
+    test('0 分 → "0.00"', () {
+      expect(yuanFromMinor(0), '0.00');
+    });
+
+    test('个位/十位/百位不加逗号', () {
+      expect(yuanFromMinor(5), '0.05');
+      expect(yuanFromMinor(99), '0.99');
+      expect(yuanFromMinor(12300), '123.00');
+    });
+
+    test('7 位数金额分组正确', () {
+      expect(yuanFromMinor(123456789), '1,234,567.89');
+    });
+
+    test('负数保留符号', () {
+      expect(yuanFromMinor(-299900), '-2,999.00');
+    });
+  });
+}