feat(tui): implement header tabs and footer help bar

draw_ui splits the terminal into header, content area, and footer.
Header shows module names as tabs with the selected one bolded and
underlined in its theme color. Footer shows keybinding hints. Both
respect the border style and chrome colors from config.

Author: dev-dami

src/tui/mod.rs

@@ -115,7 +115,102 @@ pub fn run_tui(engine: Engine, config: Config) -> Result<()> {
     Ok(())
 }
 
-fn draw_ui(_frame: &mut ratatui::Frame, _app: &App) {}
+fn draw_ui(frame: &mut ratatui::Frame, app: &App) {
+    let area = frame.area();
+    let theme = &app.config.theme;
+
+    let chrome_border = parse_color(&theme.chrome.border);
+    let chrome_title = parse_color(&theme.chrome.title);
+
+    let border_type = match app.config.tui.borders {
+        BorderStyle::None => ratatui::widgets::BorderType::Plain,
+        BorderStyle::Plain => ratatui::widgets::BorderType::Plain,
+        BorderStyle::Rounded => ratatui::widgets::BorderType::Rounded,
+    };
+
+    let chunks = Layout::default()
+        .direction(Direction::Vertical)
+        .constraints([
+            Constraint::Length(3),
+            Constraint::Min(10),
+            Constraint::Length(3),
+        ])
+        .split(area);
+
+    draw_header(frame, chunks[0], app, chrome_border, chrome_title, border_type);
+    draw_footer(frame, chunks[2], app, chrome_border, border_type);
+}
+
+fn draw_header(
+    frame: &mut ratatui::Frame,
+    area: Rect,
+    app: &App,
+    border_color: ratatui::style::Color,
+    title_color: ratatui::style::Color,
+    border_type: ratatui::widgets::BorderType,
+) {
+    let mut tabs: Vec<Span> = Vec::new();
+    if let Some(snapshot) = &app.snapshot {
+        for (i, (name, _)) in snapshot.modules.iter().enumerate() {
+            let module_color = module_fg_color(&app.config, name);
+            if i == app.selected_tab {
+                tabs.push(Span::styled(
+                    format!(" [{}] ", name.to_uppercase()),
+                    Style::default()
+                        .fg(module_color)
+                        .add_modifier(Modifier::BOLD | Modifier::UNDERLINED),
+                ));
+            } else {
+                tabs.push(Span::styled(
+                    format!("  {}  ", name.to_uppercase()),
+                    Style::default().fg(module_color),
+                ));
+            }
+        }
+    }
+
+    let header = Paragraph::new(Line::from(tabs)).block(
+        Block::default()
+            .borders(Borders::ALL)
+            .border_type(border_type)
+            .border_style(Style::default().fg(border_color))
+            .title(Span::styled(
+                " gim ",
+                Style::default()
+                    .fg(title_color)
+                    .add_modifier(Modifier::BOLD),
+            )),
+    );
+    frame.render_widget(header, area);
+}
+
+fn draw_footer(
+    frame: &mut ratatui::Frame,
+    area: Rect,
+    app: &App,
+    border_color: ratatui::style::Color,
+    border_type: ratatui::widgets::BorderType,
+) {
+    if !app.config.tui.show_help {
+        return;
+    }
+
+    let help = Paragraph::new(Line::from(vec![
+        Span::styled("q", Style::default().add_modifier(Modifier::BOLD)),
+        Span::raw(" quit  "),
+        Span::styled("←/→", Style::default().add_modifier(Modifier::BOLD)),
+        Span::raw(" switch tab  "),
+        Span::styled("Tab", Style::default().add_modifier(Modifier::BOLD)),
+        Span::raw(" next  "),
+    ]))
+    .block(
+        Block::default()
+            .borders(Borders::ALL)
+            .border_type(border_type)
+            .border_style(Style::default().fg(border_color)),
+    );
+    frame.render_widget(help, area);
+}
 
 fn module_theme<'a>(config: &'a Config, name: &str) -> &'a ModuleTheme {
     match name {