feat(cli): add --version flag and show version in help

[dlopez-bioinfo]

What

• Register a top-level --version option on the CLI group: afquery --version now prints afquery <version> instead of failing with Error: No such option '--version'.
• Show AFQuery v<version> in the group help header (afquery --help and afquery with no arguments).
• Remove the hand-maintained Commands: ... line from the group docstring; Click already renders a complete Commands: section.
• Document the global --version / --help options in the CLI reference.

Why

The installable client had no way to report its own version. The number is read from afquery.__version__, which hatch-vcs populates from the release tag at build time, so this needs no manual bump on future releases.

Tests

Added tests/test_cli.py coverage for --version, the help header, and the command listing. Full suite green locally (603 passed).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.69%. Comparing base (6c27849) to head (f34d2ea).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #38      +/-   ##
==========================================
+ Coverage   88.67%   88.69%   +0.01%     
==========================================
  Files          22       22              
  Lines        3073     3077       +4     
  Branches      482      482              
==========================================
+ Hits         2725     2729       +4     
  Misses        229      229              
  Partials      119      119              

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[dlopez-bioinfo]

Notes / known limitations:

• Editable installs: --version reads afquery.__version__ from the hatch-vcs _version.py, which is frozen at build time. pip install -e . checkouts that have advanced since the last build will show a stale number. Installable artifacts (PyPI wheel, Docker image, tag builds) are exact. importlib.metadata was considered and is no better here.
• version naming: the global --version flag now sits alongside the existing version subcommand group (database version label). Renaming that group (e.g. db-version) would be a breaking CLI change and is left as a possible follow-up.