feat: implement unified toggle widget shortcut system across interfaces

[umutdz]

Implement Toggle Widget Shortcut for All Interfaces, issue #22

This PR implements a unified toggle widget shortcut system across both Textual and Tkinter interfaces. The shortcut can be configured in settings and will be automatically converted between Textual and Tkinter formats.

Changes

• Created shortcuts.py utility in _lib folder with conversion functions:

  • convert_to_textual_shortcut: Converts Tkinter format (<Control-t>) to Textual format (ctrl+t)
  • convert_to_tkinter_shortcut: Converts Textual format to Tkinter format
  • Added comprehensive test suite in test_shortcuts.py

• Updated Tkinter interface to use the shortcut from settings:

  • secret_entry.py: Now uses toggle_widget from settings instead of hardcoded <Control-t>
  • date_entry.py: Now uses toggle_widget from settings instead of hardcoded <Control-Shift-C>

• Textual interface was already using the correct format, no changes needed

Testing

• Added test suite for shortcut conversion functions, see test_shortcuts.py

• Verified that shortcuts work in both interfaces:

  • Secret tag visibility toggle
  • File picker dialog
  • Datetime dialog

Notes

• Textual format (ctrl+t) is used as the canonical format in settings
• Automatic conversion between formats ensures consistent behavior across interfaces
• All tests are passing