tkinter rejects Cyrillic chars in bind(). Use keycode-based
<Control-Key> dispatch instead (same approach as terminal_widget).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
tk.Entry has no built-in undo (unlike tk.Text), so _entry.config(undo=True)
crashed. Replaced with custom entry_undo.py that tracks history manually
and binds Ctrl+Z/Ctrl+Y (+ Russian layout support).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>