fix(dock): drop hover_zone's children method, gone from iced's Widget trait

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014ihuqzxdUhd9UbioPn5MGu

src/ui/hover_zone.rs

@@ -49,10 +49,6 @@ impl Widget<Message, Theme, Renderer> for HoverZone<'_> {
         tree::State::new(State::default())
     }
 
-    fn children(&self) -> Vec<Tree> {
-        vec![Tree::new(&self.content)]
-    }
-
     fn diff(&mut self, tree: &mut Tree) {
         tree.diff_children(std::slice::from_mut(&mut self.content));
     }