Center VoiceFAB on all tabs

- Changed positioning from right-aligned to centered
- FAB now appears in the center above the tab bar on all screens

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

Co-Authored-By: Claude <noreply@anthropic.com>

components/VoiceFAB.tsx

@@ -123,7 +123,9 @@ export function VoiceFAB({ onPress, style, disabled = false }: VoiceFABProps) {
 const styles = StyleSheet.create({
   container: {
     position: 'absolute',
-    right: 16,
+    left: 0,
+    right: 0,
+    alignItems: 'center',
     zIndex: 100,
   },
   fab: {