Toolbar: Undo button next to Tidy Layout

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app_state.py

@@ -8,7 +8,7 @@ so later rebinding would only ever be seen by the module that did it.
 import configparser
 import os
 
-VERSION = "0.0.0.161"
+VERSION = "0.0.0.162"
 PROPERTIES_FILE = os.path.join(os.path.dirname(os.path.abspath(__file__)), "editor.properties")
 DEFAULT_GRID_SIZE = 10
 DEFAULT_ADD_TIMESTAMP = True

main.py

@@ -3038,6 +3038,11 @@ _btn_tidy = ttk.Button(toolbar, text="⊞", width=3, command=do_tidy_layout)
 _btn_tidy.pack(side=tk.LEFT, padx=(3, 0))
 _ToolTip(_btn_tidy, "Tidy Layout (Ctrl+W)")
 
+# U+21B6: anticlockwise arrow, the usual undo glyph.
+_btn_undo = ttk.Button(toolbar, text="↶", width=3, command=do_undo)
+_btn_undo.pack(side=tk.LEFT, padx=(3, 0))
+_ToolTip(_btn_undo, f"Undo ({accel_mod}+Z)")
+
 ttk.Separator(toolbar, orient=tk.VERTICAL).pack(side=tk.LEFT, fill=tk.Y, padx=8, pady=2)
 
 _btn_print = ttk.Button(toolbar, text="🖨", width=3, command=wiresheet.print_sheet)