fix: fetch sandbox metrics immediately on page load

Metrics data was only fetched after Chart.js dynamic import completed,
leaving graphs empty until the first poll interval fired. Now
loadMetrics() runs in parallel with the Chart.js import, and
initCharts() resets the dedup key so pre-fetched data populates
newly created chart instances.

frontend/src/routes/dashboard/capsules/[id]/+page.svelte

@@ -333,6 +333,7 @@
 			},
 		});
 
+		lastDataKey = '';
 		updateCharts();
 	}
 
@@ -376,6 +377,7 @@
 
 		if (!metricsAvailable) return;
 
+		loadMetrics();
 		const mod = await import('chart.js/auto');
 		ChartJS = mod.Chart;