fix: Restore missing Canvas and related r3f imports in Scene.tsx

frontend/src/components/Scene.tsx

@@ -1,7 +1,8 @@
 /**
  * Main 3D Scene component
  */
-import { Html } from '@react-three/drei';
+import { Canvas } from '@react-three/fiber';
+import { OrbitControls, Stars as BackgroundStars, Html } from '@react-three/drei';
 import { useMemo, useState, useEffect } from 'react';
 import { CelestialBody } from './CelestialBody';
 import { Probe } from './Probe';