fix(send): dismiss payment completed screen when app is backgrounded

The SendBitcoinCompletedScreen had no awareness of app lifecycle events,
so it would persist indefinitely if the user paid in-store, left the app,
and returned later — showing a stale confirmation screen.

Added an AppState listener that tracks the active → background transition
and navigates home when the app is backgrounded. Follows the same pattern
as AppStateWrapper (useRef for previous state, explicit transition check).

Closes blinkbitcoin/blink-wip#554

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: designsats

app/screens/send-bitcoin-screen/send-bitcoin-completed-screen.tsx

@@ -353,7 +353,10 @@ const SendBitcoinCompletedScreen: React.FC<Props> = ({ route }) => {
     }
   }, [feedbackShownData?.data?.feedbackModalShown, requestFeedback])
 
-  const handleNavigateHome = useCallback(() => navigation.navigate("Primary"), [navigation])
+  const handleNavigateHome = useCallback(
+    () => navigation.navigate("Primary"),
+    [navigation],
+  )
 
   const appState = useRef(AppState.currentState)
   useEffect(() => {