v1.8.12: fix Ctrl+Z undo — manual implementation for tk.Entry

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>

gui/tabs/files_tab.py

@@ -13,6 +13,7 @@ from tkinter import messagebox, filedialog
 import customtkinter as ctk
 
 from core.i18n import t
+from gui.widgets.entry_undo import enable_undo
 from core.ssh_client import SFTPSession
 from gui.widgets.file_list import FileListWidget
 
@@ -131,8 +132,7 @@ class FilesTab(ctk.CTkFrame):
         self._local_path_entry = ctk.CTkEntry(left_header, height=28)
         self._local_path_entry.pack(side="left", fill="x", expand=True, padx=(4, 0))
         self._local_path_entry.bind("<Return>", lambda e: self._local_go_to_path())
-        # Enable undo functionality
-        self._local_path_entry._entry.config(undo=True)
+        enable_undo(self._local_path_entry)
 
         self._local_list = FileListWidget(
             left_pane,
@@ -179,8 +179,7 @@ class FilesTab(ctk.CTkFrame):
         self._remote_path_entry = ctk.CTkEntry(right_header, height=28)
         self._remote_path_entry.pack(side="left", fill="x", expand=True, padx=(4, 0))
         self._remote_path_entry.bind("<Return>", lambda e: self._remote_go_to_path())
-        # Enable undo functionality
-        self._remote_path_entry._entry.config(undo=True)
+        enable_undo(self._remote_path_entry)
 
         self._remote_list = FileListWidget(
             right_pane,

gui/tabs/totp_tab.py

@@ -6,6 +6,7 @@ Live countdown, one-click copy, per-server secrets.
 import threading
 import customtkinter as ctk
 from core.i18n import t
+from gui.widgets.entry_undo import enable_undo
 
 
 class TOTPTab(ctk.CTkFrame):
@@ -106,8 +107,7 @@ class TOTPTab(ctk.CTkFrame):
             font=ctk.CTkFont(family="Consolas", size=12)
         )
         self.secret_entry.pack(side="left", fill="x", expand=True, padx=(0, 5))
-        # Enable undo functionality
-        self.secret_entry._entry.config(undo=True)
+        enable_undo(self.secret_entry)
 
         self.show_secret_btn = ctk.CTkButton(
             entry_row, text=t("show"), width=70,