Replace Ctrl+Tab with Ctrl+Left/Right for cycling lists

Ctrl+Right selects next list, Ctrl+Left selects previous list,
works from any Focus (Tabs/TaskList/Detail).

src/app.rs

@@ -187,6 +187,22 @@ impl App {
             return;
         }
 
+        if key.code == KeyCode::Right && key.modifiers.contains(KeyModifiers::CONTROL) {
+            if !self.lists.is_empty() && self.selected_list + 1 < self.lists.len() {
+                self.selected_list += 1;
+                self.load_tasks();
+            }
+            return;
+        }
+
+        if key.code == KeyCode::Left && key.modifiers.contains(KeyModifiers::CONTROL) {
+            if !self.lists.is_empty() && self.selected_list > 0 {
+                self.selected_list -= 1;
+                self.load_tasks();
+            }
+            return;
+        }
+
         match key.code {
             KeyCode::Tab => {
                 self.focus = match self.focus {