Update (or remove) command line interface

Summary

deeplabcut/cli.py is currently stale/unmaintained/outdated and not integrated with the PyTorch-first API. The Click-based CLI exposes workflow commands (create_new_project, extract_frames, train_network, analyze_videos, etc.) that currently bypass deeplabcut.compat and call pose_estimation_tensorflow directly, so they do not follow engine selection used by the public API.

In addition:

• cli.py is not really documented or tested
• click is not declared in pyproject.toml dependencies
• version banner prints deeplabcut v0.0., and --verbose is unused

Proposed direction

• As our documentation primarily mentions the python API and GUI as entry points, we should consider removing cli.py. It is currently not functional and can lead to confusion.
• We could decide (e.g. after dropping TensorFlow) to create a new command line interface that matches the PyTorch API. This does not necessarily have to use Click - there are good alternatives (e.g. Typer).