feat(review): request a store review after a 3-star win, once

Adds an in-app review prompt gated by ReviewPromptPolicy: only after a
3-star stage win, once the player has cleared >=5 stages, at most once
ever (persisted reviewRequested flag). ReviewService swallows all
failures and only burns the one-shot when the store actually shows the
sheet, so an unavailable store retries on a later win. StoreReviewer
wraps in_app_review behind a Reviewer seam so unit tests skip platform
channels. 13 new tests; full suite 194 green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/ui/screens/game_screen.dart

@@ -175,6 +175,12 @@ class _GameScreenState extends ConsumerState<GameScreen>
                   movesUsed: next.moveLimit - next.movesLeft,
                 );
           }
+          // recordWin (above) has already updated progress synchronously, so
+          // the policy's cleared-stage count includes this win. Fire-and-forget
+          // — a review prompt must never block the result card.
+          ref
+              .read(reviewServiceProvider)
+              .maybeRequestAfterWin(stars: next.starsEarned);
         }
         final stackBox =
             _stackKey.currentContext?.findRenderObject() as RenderBox?;