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/ui.rs

@@ -0,0 +1,26 @@
+use crate::app::App;
+
+pub fn render(frame: &mut ratatui::Frame, _app: &App) {
+    use ratatui::layout::{Constraint, Layout};
+    use ratatui::widgets::{Block, Borders, Paragraph};
+
+    let chunks = Layout::vertical([
+        Constraint::Length(1),
+        Constraint::Min(1),
+        Constraint::Length(1),
+    ])
+    .split(frame.area());
+
+    frame.render_widget(
+        Paragraph::new(" Log Viewer").style(ratatui::style::Style::default().bold()),
+        chunks[0],
+    );
+
+    // Main area — 使用 Block::new()（ratatui 0.30 推荐风格）
+    frame.render_widget(
+        Block::new().borders(Borders::ALL).title("No file loaded"),
+        chunks[1],
+    );
+
+    frame.render_widget(Paragraph::new(" Press '?' for help | q to quit"), chunks[2]);
+}