feat: ask for a review after a success, not at launch

[blckntr]

The review prompt showed at launch, after 10 launches over 10 days. It now shows right after a code worked:

• Reply read in the app (direct mode, Android 8+): when the run sheet closes, not over the operator's reply.
• Code handed to the phone app (called, or typed in the dialer): when the user comes back to the app (AppLifecycleListener in the reviewPrompt provider). A reply continued in the dialer waits for the return too.
• Copied codes and failures don't count.

As before, it is asked once in the app's life (reviewRequested), never after every code, and Play limits how often the sheet actually appears. Only for someone who uses the app: 5 launches, at least 3 days after the first. If the flow can't run, the next code that works tries again. The privacy policy stays accurate (first launch date and launch count, used to pick the moment).

Tests: test/services/review_prompt_test.dart rewritten (launch never asks, both moments, the dialer case, the thresholds, once only, retry). On the emulator, dialing a code doesn't ask while the dialer is in front, and coming back to the app reaches Play Core's requestInAppReview. The emulator has no Play Store, so the sheet itself can't show, and the in-app reply needs a real SIM.