feat(tui): display key hints in status bar and bind “?” to open help

- Add placeholder span showing shortcuts (i:Insert, m:Model, ?:Help, : Command) in the UI footer.
- Insert help section describing Enter key behavior in normal and insert modes.
- Extend F1 help shortcut to also trigger on “?” key (with no or Shift modifier).

crates/owlen-tui/src/ui.rs

@@ -1336,6 +1336,12 @@ fn render_status(frame: &mut Frame<'_>, area: Rect, app: &ChatApp) {
         app.current_provider().to_string(),
         Style::default().fg(theme.text),
     ));
+    spans.push(Span::styled(
+        "  i:Insert  m:Model  ?:Help  : Command",
+        Style::default()
+            .fg(theme.placeholder)
+            .add_modifier(Modifier::ITALIC),
+    ));
     spans.push(Span::styled("  ", Style::default().fg(theme.text)));
     spans.push(Span::styled(
         "Model: ",
@@ -2007,6 +2013,13 @@ fn render_help(frame: &mut Frame<'_>, app: &ChatApp) {
             Line::from("  o             → insert line below and enter insert mode"),
             Line::from("  O             → insert line above and enter insert mode"),
             Line::from(""),
+            Line::from(vec![Span::styled(
+                "ENTER KEY BEHAVIOUR",
+                Style::default().add_modifier(Modifier::BOLD).fg(theme.info),
+            )]),
+            Line::from("  Normal mode   → press Enter to send the current message"),
+            Line::from("  Insert mode   → Enter sends · Shift+Enter inserts newline"),
+            Line::from(""),
             Line::from(vec![Span::styled(
                 "INSERT MODE KEYS",
                 Style::default().add_modifier(Modifier::BOLD).fg(theme.info),