feat(mobile): add close button to planting confirm dialog

🤖 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/widgets/planting_confirm_dialog.dart

@@ -84,6 +84,11 @@ class _PlantingConfirmDialogState extends State<PlantingConfirmDialog> {
     }
   }
 
+  /// 关闭弹窗
+  void _handleClose() {
+    Navigator.pop(context, false);
+  }
+
   @override
   Widget build(BuildContext context) {
     return Dialog(
@@ -104,7 +109,10 @@ class _PlantingConfirmDialogState extends State<PlantingConfirmDialog> {
             ),
           ],
         ),
-        child: Padding(
+        child: Stack(
+          children: [
+            // 主内容
+            Padding(
               padding: const EdgeInsets.symmetric(horizontal: 24, vertical: 32),
               child: Column(
                 mainAxisSize: MainAxisSize.min,
@@ -126,6 +134,29 @@ class _PlantingConfirmDialogState extends State<PlantingConfirmDialog> {
                 ],
               ),
             ),
+            // 右上角关闭按钮
+            Positioned(
+              top: 8,
+              right: 8,
+              child: GestureDetector(
+                onTap: _handleClose,
+                child: Container(
+                  width: 32,
+                  height: 32,
+                  decoration: BoxDecoration(
+                    color: const Color(0x0D000000),
+                    borderRadius: BorderRadius.circular(16),
+                  ),
+                  child: const Icon(
+                    Icons.close,
+                    size: 18,
+                    color: Color(0xFF8B5A2B),
+                  ),
+                ),
+              ),
+            ),
+          ],
+        ),
       ),
     );
   }