fix(metrics): improve chart management in metrics dashboard

- Added logic to destroy existing charts before creating new ones, preventing memory leaks and ensuring proper chart updates.
- Updated the currentCharts object to maintain references to the newly created charts, enhancing the management of chart instances.
- These changes improve the performance and reliability of the metrics dashboard by ensuring that charts are correctly handled during updates.

internal/handler/metrics.go

@@ -700,7 +700,13 @@ var metricsTemplate = `
                 };
                 chartInstance.update();
             } else {
-                chartInstance = new Chart(ctx, {
+                // 创建新图表前先销毁旧的
+                if (currentCharts[canvasId.replace('Chart', '')]) {
+                    currentCharts[canvasId.replace('Chart', '')].destroy();
+                }
+                
+                // 创建新图表
+                const newChart = new Chart(ctx, {
                     type: 'line',
                     data: chartData,
                     options: {
@@ -722,6 +728,9 @@ var metricsTemplate = `
                         }
                     }
                 });
+
+                // 更新 currentCharts 对象
+                currentCharts[canvasId.replace('Chart', '')] = newChart;
             }
         }