Add j/k shortcuts for scrolling and update help instructions in TUI

fixes #18

crates/owlen-tui/src/chat_app.rs

@@ -328,10 +328,12 @@ impl ChatApp {
                         self.mode = InputMode::Editing;
                         self.sync_buffer_to_textarea();
                     }
-                    (KeyCode::Up, KeyModifiers::NONE) => {
+                    (KeyCode::Up, KeyModifiers::NONE)
+                    | (KeyCode::Char('k'), KeyModifiers::NONE) => {
                         self.on_scroll(-1isize);
                     }
-                    (KeyCode::Down, KeyModifiers::NONE) => {
+                    (KeyCode::Down, KeyModifiers::NONE)
+                    | (KeyCode::Char('j'), KeyModifiers::NONE) => {
                         self.on_scroll(1isize);
                     }
                     (KeyCode::Esc, KeyModifiers::NONE) => {

crates/owlen-tui/src/ui.rs

@@ -849,6 +849,8 @@ fn render_help(frame: &mut Frame<'_>) {
         Line::from("  i / Enter   → start typing"),
         Line::from("  Enter       → send message"),
         Line::from("  Ctrl+J      → newline"),
+        Line::from("  j / ↓       → scroll down"),
+        Line::from("  k / ↑       → scroll up"),
         Line::from("  m           → select model"),
         Line::from("  n           → new conversation"),
         Line::from("  c           → clear conversation"),