fix: LeafViewerHero gates heroes to the settled page (keep-alive neighbours flew too); video controls bar bottom-anchored with natural height (was stretched full-screen, blocking gestures)

lib/src/viewer/leaf_viewer.dart

@@ -94,6 +94,11 @@ class LeafViewer extends StatefulWidget {
     return LeafViewerScope.maybeOf(context)?.registry.activeController;
   }
 
+  /// The index of the page this context belongs to, if inside a viewer.
+  static int? pageIndexOf(BuildContext context) {
+    return LeafPageIndexScope.maybeOf(context);
+  }
+
   /// Reactive index of the currently settled page, if inside a viewer.
   static ValueListenable<int>? currentIndexListOf(BuildContext context) {
     return LeafViewerScope.maybeOf(context)?.currentIndex;
@@ -393,6 +398,33 @@ class _LeafViewerState extends State<LeafViewer> with TickerProviderStateMixin i
   }
 }
 
+/// A [Hero] that only participates on the viewer's currently active page.
+///
+/// LeafViewer keeps neighbour pages alive, so an unconditional hero on every
+/// page registers several per route — popping the viewer then flies the
+/// active page AND its neighbours back to the grid. This gates the hero on
+/// "this page is the settled one", so exactly one flight happens. The child
+/// instance is passed through untouched, so providers stay stable across
+/// page changes. Outside a viewer it behaves like a plain [Hero].
+class LeafViewerHero extends StatelessWidget {
+  const LeafViewerHero({super.key, required this.tag, required this.child});
+
+  final Object tag;
+  final Widget child;
+
+  @override
+  Widget build(BuildContext context) {
+    final index = LeafViewer.pageIndexOf(context);
+    final currentIndex = LeafViewer.currentIndexListOf(context);
+    if (index == null || currentIndex == null) return Hero(tag: tag, child: child);
+    return ValueListenableBuilder<int>(
+      valueListenable: currentIndex,
+      child: child,
+      builder: (context, current, child) => current == index ? Hero(tag: tag, child: child!) : child!,
+    );
+  }
+}
+
 class _LeafViewerDefaultControls extends StatelessWidget {
   const _LeafViewerDefaultControls({required this.controls, this.showPageCounter = true});