ci(gen_cli_help_screenshots): refactor the script and add some TODOs

[bearomorphism]

What is changed

• Used pathlib
• Added some TODOs (which were originally proposed by @Lee-W on 2026/01/31 scisprint)

Steps to Test This Pull Request

Run uv run poe doc:screenshots to ensure everything is still working.

The output on my machine is:

(commitizen-py3.14) (base) ➜  commitizen git:(master) ✗ uv run poe doc:screenshots
Uninstalled 2 packages in 1ms
Installed 1 package in 3ms
Poe => doc:screenshots
Uninstalled 2 packages in 1ms
Installed 1 package in 3ms
Processing command: cz --help
Saved to: /Users/bearomorphism/workspace/commitizen/docs/images/cli_help/cz___help.svg
Processing command: cz init --help
Saved to: /Users/bearomorphism/workspace/commitizen/docs/images/cli_help/cz_init___help.svg
Processing command: cz commit --help
Saved to: /Users/bearomorphism/workspace/commitizen/docs/images/cli_help/cz_commit___help.svg
Processing command: cz ls --help
Saved to: /Users/bearomorphism/workspace/commitizen/docs/images/cli_help/cz_ls___help.svg
Processing command: cz example --help
Saved to: /Users/bearomorphism/workspace/commitizen/docs/images/cli_help/cz_example___help.svg
Processing command: cz info --help
Saved to: /Users/bearomorphism/workspace/commitizen/docs/images/cli_help/cz_info___help.svg
Processing command: cz schema --help
Saved to: /Users/bearomorphism/workspace/commitizen/docs/images/cli_help/cz_schema___help.svg
Processing command: cz bump --help
Saved to: /Users/bearomorphism/workspace/commitizen/docs/images/cli_help/cz_bump___help.svg
Processing command: cz changelog --help
Saved to: /Users/bearomorphism/workspace/commitizen/docs/images/cli_help/cz_changelog___help.svg
Processing command: cz check --help
Saved to: /Users/bearomorphism/workspace/commitizen/docs/images/cli_help/cz_check___help.svg
Processing command: cz version --help
Saved to: /Users/bearomorphism/workspace/commitizen/docs/images/cli_help/cz_version___help.svg