fix(mobile): add 5s delay before confirm-province-city API call

Backend requires 5 seconds wait time after selectProvinceCity before
confirmProvinceCity can be called. Added delay to comply with this rule.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/mobile-app/lib/features/planting/presentation/pages/planting_location_page.dart

@@ -132,10 +132,14 @@ class _PlantingLocationPageState extends ConsumerState<PlantingLocationPage> {
         cityName: _selectedCityName!,
       );
 
-      // 2. 确认省市选择
+      // 2. 等待5秒后确认省市选择（后端要求等待5秒确认时间）
+      debugPrint('[PlantingLocationPage] 等待5秒确认时间...');
+      await Future.delayed(const Duration(seconds: 5));
+
+      // 3. 确认省市选择
       await plantingService.confirmProvinceCity(widget.orderNo);
 
-      // 3. 支付订单
+      // 4. 支付订单
       await plantingService.payOrder(widget.orderNo);
 
       if (mounted) {