fix(tui): correct cursor position in input fields

Fixed cursor position calculation in TUI input components. The cursor
was appearing on top of the last character instead of after it due to
incorrect offset calculation.

Changes:
- app.rs: Fixed cursor position from area.x + 2 to area.x + 3
  (accounting for left border + "> " prefix)
- widgets/input.rs: Same fix for CommandInput widget
- components/text_input.rs: Show underline cursor at end of text

Co-Authored-By: Claude Opus 4.6 <noreply@openkeyring.com>

Author: p1024k

src/tui/app.rs

@@ -1085,8 +1085,8 @@ impl TuiApp {
 
         frame.render_widget(paragraph, area);
 
-        // Set cursor position
-        frame.set_cursor_position((area.x + 2 + self.input_buffer.len() as u16, area.y + 1));
+        // Set cursor position (area.x + 1 for left border, + 2 for "> " prefix, then cursor offset)
+        frame.set_cursor_position((area.x + 3 + self.input_buffer.len() as u16, area.y + 1));
     }
 }
 

src/tui/components/text_input.rs

@@ -225,9 +225,16 @@ impl Render for TextInput {
         if self.focused && area.width > 0 {
             let cursor_x = self.cursor.min(area.width as usize - 1);
             // 光标位置用下划线表示
+            // Note: cursor_x is byte offset, but for ASCII it equals display width
             if self.cursor < self.text.len() {
+                // Cursor within text - underline the character at cursor position
                 buf[(area.x + cursor_x as u16, area.y)]
                     .set_style(style.add_modifier(Modifier::UNDERLINED));
+            } else {
+                // Cursor at end of text - show underline cursor in empty space
+                buf[(area.x + cursor_x as u16, area.y)]
+                    .set_char(' ')
+                    .set_style(style.add_modifier(Modifier::UNDERLINED));
             }
         }
     }

src/tui/widgets/input.rs

@@ -155,7 +155,7 @@ impl CommandInput {
 
         frame.render_widget(paragraph, area);
 
-        // Set cursor position
-        frame.set_cursor_position((area.x + 2 + self.cursor as u16, area.y + 1));
+        // Set cursor position (area.x + 1 for left border, + 2 for "> " prefix, then cursor offset)
+        frame.set_cursor_position((area.x + 3 + self.cursor as u16, area.y + 1));
     }
 }