Multi-select tasks with Shift+Arrows and bulk actions

- Shift+Up/Down extends selection in task list
- Enter opens BulkAction popup with 3 options:
  1. Mark as completed
  2. Set due date to Today
  3. Move to new list (creates list, copies tasks, deletes originals)
- Plain Up/Down clears selection, Escape clears it
- Selected items highlighted in Yellow

src/ui/components.rs

@@ -1,3 +1,5 @@
+use std::collections::BTreeSet;
+
 use chrono::Datelike;
 
 use ratatui::style::{Color, Modifier, Style};
@@ -76,6 +78,7 @@ pub fn render_task_list(
     selected: usize,
     focused: bool,
     _scroll: u16,
+    selected_tasks: &BTreeSet<usize>,
 ) {
     let total = tasks.len();
     let done = tasks.iter().filter(|t| t.status == TaskStatus::Completed).count();
@@ -85,7 +88,9 @@ pub fn render_task_list(
 
     let items: Vec<ListItem> = tasks
         .iter()
-        .map(|task| {
+        .enumerate()
+        .map(|(idx, task)| {
+            let is_selected = selected_tasks.contains(&idx);
             let checkbox = match task.status {
                 TaskStatus::Completed => "[\u{2713}]",
                 TaskStatus::NeedsAction => "[ ]",
@@ -121,25 +126,29 @@ pub fn render_task_list(
                 content_width.saturating_sub(used)
             };
 
-            let mut spans = vec![
-                Span::styled(
-                    checkbox_str,
-                    Style::default().fg(if task.status == TaskStatus::Completed {
-                        Color::Green
+            let checkbox_style = if is_selected {
+                Style::default().fg(Color::Yellow).add_modifier(Modifier::BOLD)
+            } else if task.status == TaskStatus::Completed {
+                Style::default().fg(Color::Green)
+            } else {
+                Style::default().fg(Color::DarkGray)
+            };
+
+            let title_style = if is_selected {
+                Style::default().fg(Color::Yellow).add_modifier(Modifier::BOLD)
+            } else {
+                Style::default().fg(DETAIL_COLOR).add_modifier(
+                    if task.status == TaskStatus::Completed {
+                        Modifier::CROSSED_OUT
                     } else {
-                        Color::DarkGray
-                    }),
-                ),
-                Span::styled(
-                    display_title,
-                    Style::default().fg(DETAIL_COLOR).add_modifier(
-                        if task.status == TaskStatus::Completed {
-                            Modifier::CROSSED_OUT
-                        } else {
-                            Modifier::empty()
-                        },
-                    ),
-                ),
+                        Modifier::empty()
+                    },
+                )
+            };
+
+            let mut spans = vec![
+                Span::styled(checkbox_str, checkbox_style),
+                Span::styled(display_title, title_style),
             ];
 
             if !due_text.is_empty() {
@@ -498,6 +507,44 @@ pub fn render_confirm_popup(frame: &mut Frame, area: Rect) {
     frame.render_widget(paragraph, popup_area);
 }
 
+pub fn render_bulk_action_popup(frame: &mut Frame, area: Rect, count: usize) {
+    let popup_area = centered_rect(55, 9, area);
+    frame.render_widget(Clear, popup_area);
+    let block = Block::default()
+        .borders(Borders::ALL)
+        .style(Style::default().bg(POPUP_BG))
+        .border_style(Style::default().fg(POPUP_BORDER))
+        .title(format!(" Bulk Actions ({} selected) ", count))
+        .title_alignment(Alignment::Left);
+
+    let text = Text::from(vec![
+        Line::from(""),
+        Line::from(Span::styled(
+            "  1. Mark as completed",
+            Style::default().fg(Color::Cyan),
+        )),
+        Line::from(Span::styled(
+            "  2. Set due date to Today",
+            Style::default().fg(Color::Cyan),
+        )),
+        Line::from(Span::styled(
+            "  3. Move to new list...",
+            Style::default().fg(Color::Cyan),
+        )),
+        Line::from(""),
+        Line::from(Span::styled(
+            "  Press 1-3 or Esc to cancel",
+            Style::default().fg(Color::DarkGray),
+        )),
+    ]);
+
+    let paragraph = Paragraph::new(text)
+        .block(block)
+        .alignment(Alignment::Left);
+
+    frame.render_widget(paragraph, popup_area);
+}
+
 pub fn render_device_auth_popup(
     frame: &mut Frame,
     area: Rect,