[FR] Add --version flag to tkdesigner CLI

Use case

Users filing bug reports and maintainers triaging them need the installed tkdesigner version. Currently the only path is pip show tkdesigner, which fails inside virtualenvs users forget they activated.

Proposal

Add --version / -V to argparse in tkdesigner/cli.py:

from tkdesigner import __version__
parser.add_argument('--version', action='version', version=f'tkdesigner {__version__}')

Requires exposing __version__ in tkdesigner/__init__.py (currently empty per repo listing).

Existing art

Standard argparse pattern; used by pip, black, poetry.

Not-a-bug caveat

Cosmetic/DX improvement, not a defect.

Thanks for maintaining ParthJadhav/Tkinter-Designer!