fix: hide ECharts toolbox in sandbox metrics chart (#460)

## Summary

The sandbox detail monitoring chart (`SandboxMetricsChart`) registers
`ToolboxComponent` (required for brush/zoom), but unlike
`team-metrics-chart` and `compute-usage-chart`, it was missing `toolbox:
{ show: false }` in its ECharts option. This caused the toolbox icons
(brush, zoom, reset, etc.) to render visibly in the top-right corner of
the chart.

With Turbopack this defaulted to hidden due to different module
initialization order, but Webpack renders the toolbox visibly.

```diff
 return {
   backgroundColor: 'transparent',
   animation: false,
+  toolbox: { show: false },
   brush: isMobile ? undefined : { ... },
```

Link to Devin session:
https://app.devin.ai/sessions/26cc0135d9e24aaa87881e8d7e2069cb

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: ben@e2b.dev <ben@e2b.dev>

Author: devin-ai-integration[bot]

src/features/dashboard/sandbox/monitoring/components/monitoring-sandbox-metrics-chart.tsx

@@ -467,6 +467,9 @@ function SandboxMetricsChart({
     return {
       backgroundColor: 'transparent',
       animation: false,
+      toolbox: {
+        show: false,
+      },
       brush: isMobile
         ? undefined
         : {