feat(app): keyboard event handling with panel switching and CRUD

- App struct with full state (lists, tasks, focus, popups, DB)
- Tab cycles focus: Tabs -> TaskList -> Detail -> Tabs
- Left/Right arrows switch lists when focus on Tabs
- Up/Down navigate tasks (TaskList) or scroll (Detail)
- Alt+Up/Down reorder tasks with position persistence
- n: create new list or task, d: delete, e: edit title
- Enter on Detail opens DatePicker popup
- InputPopup with full text editing (navigation, insert, delete)
- ConfirmDelete popup before destructive actions
- DatePicker adjusts draft_date with Up/Down
- main.rs: terminal setup, event loop, raw mode, alternate screen

src/main.rs

@@ -1,7 +1,63 @@
+mod app;
 mod domain;
-mod ui;
 mod infrastructure;
+mod ui;
 
-fn main() {
-    println!("Task App - Google Tasks TUI");
+use std::io;
+
+use crossterm::event::{self, Event};
+use crossterm::terminal::{disable_raw_mode, enable_raw_mode, EnterAlternateScreen, LeaveAlternateScreen};
+use crossterm::ExecutableCommand;
+use ratatui::backend::CrosstermBackend;
+use ratatui::Terminal;
+
+use crate::app::App;
+use crate::infrastructure::db::Db;
+use crate::ui::{draw, AppView};
+
+fn main() -> io::Result<()> {
+    let db_path = dirs::data_dir()
+        .unwrap_or_else(|| std::path::PathBuf::from("."))
+        .join("task_app")
+        .join("tasks.db");
+
+    std::fs::create_dir_all(db_path.parent().unwrap()).ok();
+
+    let db = Db::new(db_path.to_str().unwrap()).expect("Failed to open database");
+
+    enable_raw_mode()?;
+    let mut stdout = io::stdout();
+    stdout.execute(EnterAlternateScreen)?;
+    let backend = CrosstermBackend::new(stdout);
+    let mut terminal = Terminal::new(backend)?;
+
+    let mut app = App::new(db);
+
+    while !app.should_quit {
+        terminal.draw(|frame| {
+            let view = AppView {
+                lists: &app.lists,
+                tasks: &app.tasks,
+                selected_list: app.selected_list,
+                selected_task: app.selected_task,
+                focus: app.focus.clone(),
+                show_popup: app.show_popup.as_ref(),
+                popup_input: &app.popup_input,
+                popup_cursor: app.popup_cursor,
+                draft_date: app.draft_date,
+                network_status: &app.network_status,
+                task_list_scroll: app.task_list_scroll,
+                detail_scroll: app.detail_scroll,
+            };
+            draw(frame, view);
+        })?;
+
+        if let Event::Key(key) = event::read()? {
+            app.handle_key(key);
+        }
+    }
+
+    disable_raw_mode()?;
+    io::stdout().execute(LeaveAlternateScreen)?;
+    Ok(())
 }