feat: add --version/-v flag to sql2json CLI

[fsistemas]

Summary

Adds a --version / -v flag to the sql2json CLI. Previously sql2json --version tried to run a query named version and failed with a config error.

sql2json --version
# → sql2json 0.3.0
sql2json -v
# → sql2json 0.3.0

The check runs in main() before fire.Fire(), so it short-circuits all normal query execution, prints sql2json <version> to stdout, and exits 0. Version comes from the existing __version__ (importlib.metadata).

Tests

New TestVersion class in tests/test_cli.py (runs the real CLI as a subprocess):

• --version and -v each exit 0 and print sql2json <version>
• no query runs / stderr is empty
• short-circuits before config is read (works with a missing --config path)
• works when combined with other flags (--name/--query)

Version is asserted against sql2json.__version__, so tests survive version bumps. Full suite (145) and flake8 pass.

Docs

Updated README.md, AGENTS.md, skills/sql2json/SKILL.md, and CHANGELOG.md (Unreleased → Added).