Add group filtering and layout for keybindings UI

Return the set of used groups from `binding_for_view` and adjust
`keybindings_widget` to render only those groups. Introduce a vertical
layout in the main widget to display a placeholder paragraph above
the keybindings area, and update imports and border logic accordingly.

src/app/keybindings/keybindings.rs

@@ -1,5 +1,6 @@
 use crate::app::View;
 use ratatui::crossterm::event::{KeyCode, KeyEvent, KeyEventKind, KeyModifiers};
+use std::collections::HashSet;
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub enum Action {
@@ -24,10 +25,6 @@ impl Group {
             .iter()
             .copied()
     }
-
-    pub fn len() -> usize {
-        Self::iter().count()
-    }
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
@@ -109,19 +106,33 @@ pub fn event_to_action(event: &KeyEvent) -> Option<Action> {
         .map(|b| b.action)
 }
 
-pub fn binding_for_view(view: View) -> Vec<&'static KeyBinding> {
+fn used_groups_in_view(keybindings: &Vec<&'static KeyBinding>) -> HashSet<Group> {
+    keybindings.iter().map(|b| b.group).collect()
+}
+
+pub fn binding_for_view(view: View) -> (HashSet<Group>, Vec<&'static KeyBinding>) {
+    let main_menu_keybindings: Vec<&'static KeyBinding> = vec![
+        binding_for(Action::Up).unwrap(),
+        binding_for(Action::Down).unwrap(),
+        binding_for(Action::Space).unwrap(),
+        binding_for(Action::Quit).unwrap(),
+        binding_for(Action::Quit2).unwrap(),
+    ];
+
+    let default_keybindings: Vec<&'static KeyBinding> = vec![
+        binding_for(Action::Quit).unwrap(),
+        binding_for(Action::Quit2).unwrap(),
+        binding_for(Action::Esc).unwrap(),
+    ];
+
     match view {
-        View::MainMenu => vec![
-            binding_for(Action::Up).unwrap(),
-            binding_for(Action::Down).unwrap(),
-            binding_for(Action::Space).unwrap(),
-            binding_for(Action::Quit).unwrap(),
-            binding_for(Action::Quit2).unwrap(),
-        ],
-        _ => vec![
-            binding_for(Action::Quit).unwrap(),
-            binding_for(Action::Quit2).unwrap(),
-            binding_for(Action::Esc).unwrap(),
-        ],
+        View::MainMenu => (
+            used_groups_in_view(&main_menu_keybindings),
+            main_menu_keybindings,
+        ),
+        _ => (
+            used_groups_in_view(&default_keybindings),
+            default_keybindings,
+        ),
     }
 }

src/app/widget.rs

@@ -1,5 +1,13 @@
-use crate::app::{App, View, widgets::main_menu_widget};
-use ratatui::{buffer::Buffer, layout::Rect, widgets::Widget};
+use crate::app::{
+    App, View,
+    widgets::{keybindings_widget, main_menu_widget},
+};
+use ratatui::{
+    buffer::Buffer,
+    layout::{Alignment, Constraint, Layout, Rect},
+    style::Stylize,
+    widgets::{Block, Borders, Paragraph, Widget},
+};
 
 impl Widget for &App {
     fn render(self, area: Rect, buf: &mut Buffer)
@@ -8,7 +16,24 @@ impl Widget for &App {
     {
         match self.view {
             View::MainMenu => main_menu_widget(self, area, buf),
-            _ => (),
+            _ => {
+                let vertical_layout: Layout =
+                    Layout::vertical([Constraint::Fill(1), Constraint::Length(4)]);
+
+                let [main_area, keybindings_area] = vertical_layout.areas(area);
+
+                Paragraph::new("Work in progress")
+                    .alignment(Alignment::Center)
+                    .yellow()
+                    .block(
+                        Block::new()
+                            .gray()
+                            .borders(Borders::LEFT | Borders::TOP | Borders::RIGHT),
+                    )
+                    .render(main_area, buf);
+
+                keybindings_widget(self.view).render(keybindings_area, buf);
+            }
         }
     }
 }

src/app/widgets/keybindings.rs

@@ -1,6 +1,6 @@
 use crate::app::{
     View,
-    keybindings::{Group, KeyBinding, binding_for_view},
+    keybindings::{Group, binding_for_view},
 };
 use ratatui::{
     buffer::Buffer,
@@ -43,10 +43,14 @@ impl Widget for KeybindingsWidget {
 }
 
 pub fn keybindings_widget(view: View) -> KeybindingsWidget {
-    let keybindings: Vec<&'static KeyBinding> = binding_for_view(view);
+    let (used_groups, keybindings) = binding_for_view(view);
 
     let mut grouped_keybindings: Vec<Paragraph<'static>> = Vec::new();
     for (i, group) in Group::iter().enumerate() {
+        if !used_groups.contains(&group) {
+            continue;
+        }
+
         let grouped_lines: Vec<Line<'_>> = keybindings
             .iter()
             .filter(|b| b.group == group)
@@ -55,8 +59,8 @@ pub fn keybindings_widget(view: View) -> KeybindingsWidget {
 
         let mut block: Block<'_> = Block::default().padding(Padding::new(1, 1, 0, 0));
 
-        if i != Group::len() - 1 {
-            block = block.borders(Borders::RIGHT);
+        if i != 0 {
+            block = block.borders(Borders::LEFT);
         }
 
         grouped_keybindings.push(