v1.8.23: fix Ctrl+V/C/X/A/Z for non-Latin keyboard layouts, add Entry undo/redo

- Global keycode-based handler for Ctrl shortcuts (works with Russian, Chinese, any layout)
- Tkinter maps <<Paste>> to <Control-v> by keysym which fails on non-Latin layouts
- New handler intercepts <Control-Key> at 'all' level, checks keycodes and generates correct virtual events
- Added Undo/Redo support for Entry widgets (tk.Entry has no built-in undo)
- Tab switch focus management: terminal releases focus when switching away

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

gui/widgets/terminal_widget.py

@@ -251,6 +251,9 @@ class TerminalWidget(tk.Frame):
         self._selecting = False
         self._last_ctrl_c: float = 0.0
 
+        # ── Keyboard enable/disable (for modal dialogs) ──
+        self._keyboard_enabled = True
+
         # ── Flash status state ──
         self._flash_after_id = None
         self._saved_status_text = ""
@@ -360,6 +363,14 @@ class TerminalWidget(tk.Frame):
     def focus_terminal(self):
         self._text.focus_set()
 
+    def disable_keyboard(self):
+        """Disable keyboard processing (e.g. when a modal dialog is open)."""
+        self._keyboard_enabled = False
+
+    def enable_keyboard(self):
+        """Re-enable keyboard processing."""
+        self._keyboard_enabled = True
+
     def get_size(self) -> tuple[int, int]:
         return self._cols, self._rows
 
@@ -581,6 +592,9 @@ class TerminalWidget(tk.Frame):
     # ── Keyboard handling ──────────────────────────────────────────────────
 
     def _on_key(self, event):
+        # Don't intercept keys when keyboard is disabled (modal dialog open)
+        if not self._keyboard_enabled:
+            return
         # Ignore modifier-only keys
         if event.keysym in ("Shift_L", "Shift_R", "Control_L", "Control_R",
                             "Alt_L", "Alt_R", "Meta_L", "Meta_R",
@@ -708,6 +722,8 @@ class TerminalWidget(tk.Frame):
 
     def _on_ctrl_key(self, event):
         """Route Ctrl+key by physical keycode (layout-independent)."""
+        if not self._keyboard_enabled:
+            return
         handler_name = self._CTRL_KEYCODE_MAP.get(event.keycode)
         if handler_name:
             # Check if Shift is also held