fix(detail): isolate overlay sheet scrolling

lib/screens/media_detail_screen.dart

@@ -704,7 +704,9 @@ class _MediaDetailScreenState extends State<MediaDetailScreen>
   }
 
   void _onScroll() {
-    _scrollOffset.value = _scrollController.offset;
+    final positions = _scrollController.positions;
+    if (positions.length != 1) return;
+    _scrollOffset.value = positions.first.pixels;
   }
 
   @override

lib/widgets/overlay_sheet.dart

@@ -546,6 +546,8 @@ class _OverlaySheetHostState extends State<OverlaySheetHost> with SingleTickerPr
     final colorScheme = Theme.of(context).colorScheme;
 
     Widget content = _pageStack.isNotEmpty ? Builder(builder: _pageStack.last.builder) : const SizedBox.shrink();
+    // Keep sheet scrollables from attaching to the route's primary controller.
+    content = PrimaryScrollController.none(child: content);
 
     // Wrap content in NotificationListener for scroll-aware drag-to-dismiss
     if (showHandle) {

test/widgets/overlay_sheet_test.dart

@@ -0,0 +1,54 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:plezy/widgets/overlay_sheet.dart';
+
+void main() {
+  testWidgets('scrollable sheet does not attach to parent primary controller', (tester) async {
+    final parentController = ScrollController();
+    addTearDown(parentController.dispose);
+
+    await tester.pumpWidget(
+      MaterialApp(
+        theme: ThemeData(platform: TargetPlatform.android),
+        home: PrimaryScrollController(
+          controller: parentController,
+          child: OverlaySheetHost(
+            child: Scaffold(
+              body: CustomScrollView(
+                primary: true,
+                slivers: [
+                  SliverFillRemaining(
+                    child: Center(
+                      child: Builder(
+                        builder: (context) => ElevatedButton(
+                          onPressed: () {
+                            OverlaySheetController.of(context).show<void>(
+                              builder: (_) => ListView.builder(
+                                itemCount: 30,
+                                itemBuilder: (_, index) => ListTile(title: Text('Item $index')),
+                              ),
+                            );
+                          },
+                          child: const Text('Open'),
+                        ),
+                      ),
+                    ),
+                  ),
+                ],
+              ),
+            ),
+          ),
+        ),
+      ),
+    );
+
+    expect(parentController.positions.length, 1);
+
+    await tester.tap(find.text('Open'));
+    await tester.pumpAndSettle();
+
+    expect(tester.takeException(), isNull);
+    expect(parentController.positions.length, 1);
+    expect(find.text('Item 0'), findsOneWidget);
+  });
+}