feat(tui): add help overlay shortcuts (F1/?) and update help UI and status messages

- Introduced a new “HELP & QUICK COMMANDS” section with bold header and shortcuts for toggling the help overlay and opening the files panel.
- Updated command help text to “Open the help overlay”.
- Extended onboarding and tutorial status lines to display the help shortcut.
- Modified help command handling to set the status to “Help” and clear errors.

crates/owlen-tui/src/ui.rs

@@ -3061,6 +3061,14 @@ fn render_help(frame: &mut Frame<'_>, app: &ChatApp) {
             Line::from("  Ctrl+d/u      → scroll half page down/up"),
             Line::from("  Ctrl+f/b      → scroll full page down/up"),
             Line::from("  PageUp/Down   → scroll full page"),
+            Line::from(""),
+            Line::from(vec![Span::styled(
+                "HELP & QUICK COMMANDS",
+                Style::default().add_modifier(Modifier::BOLD).fg(theme.info),
+            )]),
+            Line::from("  F1 / ?        → toggle help overlay"),
+            Line::from("  :h, :help     → open help from command mode"),
+            Line::from("  :files, :explorer → toggle files panel"),
         ],
         1 => vec![
             // Editing
@@ -3171,6 +3179,8 @@ fn render_help(frame: &mut Frame<'_>, app: &ChatApp) {
                     .fg(theme.user_message_role),
             )]),
             Line::from("  :h, :help          → show this help"),
+            Line::from("  F1 or ?           → toggle help overlay"),
+            Line::from("  :files, :explorer → toggle files panel"),
             Line::from("  :quit              → quit application"),
             Line::from("  Ctrl+C twice       → quit application"),
             Line::from("  :reload            → reload configuration and themes"),