feat(tui): ratatui skeleton with layout

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

crates/tui/src/app.rs

@@ -0,0 +1,17 @@
+pub struct App {
+    pub should_quit: bool,
+}
+
+impl App {
+    pub fn new() -> Self {
+        Self { should_quit: false }
+    }
+
+    pub fn handle_key(&mut self, key: crossterm::event::KeyEvent) {
+        match key.code {
+            crossterm::event::KeyCode::Char('q') => self.should_quit = true,
+            crossterm::event::KeyCode::Esc => self.should_quit = true,
+            _ => {}
+        }
+    }
+}