fix(player): 使用根Overlay承载飘心

test/player/player_double_tap_hearts_test.dart

@@ -57,6 +57,48 @@ void main() {
     expect(_opacity(tester, 0), lessThan(0.5));
   });
 
+  testWidgets('heart position is anchored to the overlay origin', (
+    tester,
+  ) async {
+    const origin = Offset(300, 546);
+    await tester.pumpWidget(
+      const MaterialApp(
+        home: Scaffold(
+          body: Stack(
+            fit: StackFit.expand,
+            children: [
+              Positioned.fill(
+                child: PlayerDoubleTapHeartBurst(
+                  burstId: 4,
+                  origin: origin,
+                  onCompleted: _noop,
+                ),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+
+    final firstHeart = find.byKey(const Key('double-tap-heart-0'));
+    expect(
+      (tester.getCenter(firstHeart) - origin).distance,
+      lessThanOrEqualTo(1),
+    );
+    final debugTopLeft = tester.getTopLeft(
+      find.byKey(const Key('heart-burst-elapsed-debug')),
+    );
+    expect(
+      (debugTopLeft - const Offset(308, 556)).distance,
+      lessThanOrEqualTo(1),
+    );
+
+    await tester.pump(const Duration(milliseconds: 750));
+    final midpoint = tester.getCenter(firstHeart);
+    expect(midpoint.dy, lessThan(origin.dy));
+    expect((midpoint.dx - origin.dx).abs(), lessThanOrEqualTo(1));
+  });
+
   testWidgets('develop heart burst completes after about 1590ms', (
     tester,
   ) async {