feat(ui): render layout, tabs, panes, popups, and status bar

- ui/mod.rs: AppView struct, Focus/Popup/NetworkStatus enums, draw() layout function
- Top-Tabs + Bottom-Split layout (50/50 left/right)
- TabsBar: list selector with highlight on active
- TaskListPane: checkbox + title + due date per task
- DetailPane: title, status, due, notes of selected task
- InputPopup: centered modal with cursor
- DatePickerPopup: date/time edit modal with instructions
- ConfirmDeletePopup: confirmation dialog
- DeviceAuthPopup: OAuth URL + code display
- StatusBar: ONLINE/OFFLINE/SYNCING with color coding

src/ui/mod.rs

@@ -1 +1,99 @@
 pub mod components;
+
+use ratatui::layout::{Constraint, Direction, Layout};
+use ratatui::Frame;
+
+use crate::domain::models::*;
+use components::*;
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum Focus {
+    Tabs,
+    TaskList,
+    Detail,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum Popup {
+    Input,
+    DatePicker,
+    ConfirmDelete,
+    DeviceAuth { url: String, code: String },
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum NetworkStatus {
+    Online,
+    Offline,
+    Syncing,
+}
+
+pub struct AppView<'a> {
+    pub lists: &'a [TaskList],
+    pub tasks: &'a [Task],
+    pub selected_list: usize,
+    pub selected_task: usize,
+    pub focus: Focus,
+    pub show_popup: Option<&'a Popup>,
+    pub popup_input: &'a str,
+    pub popup_cursor: usize,
+    pub draft_date: chrono::NaiveDateTime,
+    pub network_status: &'a NetworkStatus,
+    pub task_list_scroll: u16,
+    pub detail_scroll: u16,
+}
+
+pub fn draw(frame: &mut Frame, view: AppView) {
+    let area = frame.area();
+
+    let main_layout = Layout::default()
+        .direction(Direction::Vertical)
+        .constraints([
+            Constraint::Length(3),
+            Constraint::Min(0),
+            Constraint::Length(1),
+        ])
+        .split(area);
+
+    let tabs_area = main_layout[0];
+    let body_area = main_layout[1];
+    let status_area = main_layout[2];
+
+    let is_tabs_focused = view.focus == Focus::Tabs;
+    render_tabs_bar(frame, tabs_area, view.lists, view.selected_list, is_tabs_focused);
+
+    let body_layout = Layout::default()
+        .direction(Direction::Horizontal)
+        .constraints([Constraint::Percentage(50), Constraint::Percentage(50)])
+        .split(body_area);
+
+    let is_task_list_focused = view.focus == Focus::TaskList;
+    render_task_list(
+        frame,
+        body_layout[0],
+        view.tasks,
+        view.selected_task,
+        is_task_list_focused,
+        view.task_list_scroll,
+    );
+
+    let is_detail_focused = view.focus == Focus::Detail;
+    render_detail(
+        frame,
+        body_layout[1],
+        view.tasks.get(view.selected_task),
+        is_detail_focused,
+        view.detail_scroll,
+    );
+
+    render_status_bar(frame, status_area, view.network_status);
+
+    if let Some(popup) = view.show_popup {
+        match popup {
+            Popup::Input => render_input_popup(frame, area, view.popup_input, view.popup_cursor),
+            Popup::DatePicker => render_date_picker(frame, area, view.draft_date),
+            Popup::ConfirmDelete => render_confirm_popup(frame, area),
+            Popup::DeviceAuth { url, code } => render_device_auth_popup(frame, area, url, code),
+        }
+    }
+}