feat: rudimentary keyboard scrolling

I want smooth scrolling :(

src/app/mod.rs

@@ -142,6 +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)
                 }
@@ -190,6 +215,7 @@ impl State {
                 }))
                 .columns(self.columns),
             )
+            .id("main")
             .height(Length::Fill)
             .into(),
             self.error.as_ref().map_or_else(