feat: rudimentary keyboard scrolling

I want smooth scrolling :(

src/app/mod.rs

@@ -44,6 +44,8 @@ struct State {
 
     columns: usize,
 
+    key: usize,
+
     error: Option<String>,
 }
 
@@ -51,9 +53,10 @@ impl State {
     fn new() -> (Self, Task<Message>) {
         (
             Self {
-                columns: 3,
-                error: None,
                 images: BTreeMap::new(),
+                columns: 3,
+                key: 0,
+                error: None,
             },
             Task::done(Message::OpenPath(Some(
                 env::args()
@@ -107,7 +110,7 @@ impl State {
                     .arg(path)
                     .spawn()
                     .map_err(|e| e.to_string())
-                    .err()
+                    .err();
             }
 
             Message::OpenPath(opt_path) => {
@@ -117,6 +120,7 @@ impl State {
                 };
 
                 if let Some(path) = opt_path {
+                    self.key += 1;
                     self.open_path(path);
                 }
             }
@@ -138,6 +142,31 @@ impl State {
                     );
                 }
 
+                keyboard::Key::Character("j")
+                | keyboard::Key::Named(
+                    keyboard::key::Named::ArrowDown | keyboard::key::Named::PageDown,
+                ) => {
+                    return widget::operation::scroll_by(
+                        "main",
+                        widget::operation::AbsoluteOffset {
+                            x: 0.,
+                            y: if modifiers.shift() { 100. } else { 30. },
+                        },
+                    );
+                }
+                keyboard::Key::Character("k")
+                | keyboard::Key::Named(
+                    keyboard::key::Named::ArrowUp | keyboard::key::Named::PageUp,
+                ) => {
+                    return widget::operation::scroll_by(
+                        "main",
+                        widget::operation::AbsoluteOffset {
+                            x: 0.,
+                            y: if modifiers.shift() { -100. } else { -30. },
+                        },
+                    );
+                }
+
                 keyboard::Key::Character("=" | "+") => {
                     self.columns = (self.columns + 1).clamp(1, 10)
                 }
@@ -164,6 +193,7 @@ impl State {
                                 || Element::from(widget::space()),
                                 |handle| widget::image(handle).into(),
                             ))
+                            .key(self.key)
                             .anticipate(2000)
                             .on_show(|_size| Message::LoadImage(path.clone()))
                             .on_hide(Message::UnloadImage(path.clone())),
@@ -185,6 +215,7 @@ impl State {
                 }))
                 .columns(self.columns),
             )
+            .id("main")
             .height(Length::Fill)
             .into(),
             self.error.as_ref().map_or_else(