fix: make Show Simulation Box checkbox toggleable (fixes #308) (#309)

## Summary

- The `useEffect` in `View.tsx` that synced
`renderSettings.showSimulationBox` with `embedConfig.showSimulationBox`
lacked an `isEmbeddedMode` guard
- Since `embedConfig.showSimulationBox` defaults to `true`, any user
toggle of the checkbox was immediately overwritten back to `true`,
making it appear permanently enabled and unclickable
- Fix: added `isEmbeddedMode &&` condition so the sync only runs when
actually in embedded mode

## Behavior after fix

- **Non-embedded mode**: checkbox is freely toggleable as expected
- **Embedded mode**: `embedConfig.showSimulationBox` (from URL params)
continues to override the setting, preserving existing behavior

## Test plan

- [ ] Open the app in normal (non-embedded) mode → verify the "Show
simulation box" checkbox in Settings can be checked/unchecked
- [ ] Open the app in embedded mode with `showSimulationBox=false` in
the URL config → verify the box is hidden and the setting is locked to
`false`
- [ ] Open the app in embedded mode with no explicit `showSimulationBox`
config (defaults to `true`) → verify the box is shown
- [ ] `npm run build` passes with no errors ✅

Closes #308

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

Author: andeplane

src/containers/View.tsx

@@ -403,15 +403,18 @@ const View = ({ visible, isEmbeddedMode = false }: ViewProps) => {
     embedConfig.enableParticlePicking,
   ]);
 
-  // Apply showSimulationBox setting from embed config
+  // Apply showSimulationBox setting from embed config (only in embedded mode)
   useEffect(() => {
-    if (renderSettings.showSimulationBox !== embedConfig.showSimulationBox) {
+    if (
+      isEmbeddedMode &&
+      renderSettings.showSimulationBox !== embedConfig.showSimulationBox
+    ) {
       setRenderSettings({
         ...renderSettings,
         showSimulationBox: embedConfig.showSimulationBox,
       });
     }
-  }, [embedConfig.showSimulationBox, renderSettings, setRenderSettings]);
+  }, [isEmbeddedMode, embedConfig.showSimulationBox, renderSettings, setRenderSettings]);
 
   // Update camera planes based on simulation box bounds
   useEffect(() => {