fix(voip): animate header background to transparent when hiding controls

The MediaCallHeader used translateY + opacity to hide, but its
surfaceNeutral background remained visible as a dark bar. Animate
backgroundColor and borderBottomColor to transparent so CallView
shows through seamlessly.

Author: diegolmello

app/containers/MediaCallHeader/MediaCallHeader.tsx

@@ -40,7 +40,9 @@ const MediaCallHeader = () => {
 					duration: CONTROLS_ANIMATION_DURATION
 				})
 			}
-		]
+		],
+		backgroundColor: withTiming(shouldHide ? 'transparent' : colors.surfaceNeutral, { duration: CONTROLS_ANIMATION_DURATION }),
+		borderBottomColor: withTiming(shouldHide ? 'transparent' : colors.strokeLight, { duration: CONTROLS_ANIMATION_DURATION })
 	}));
 
 	const defaultHeaderStyle = {