Add --version flag to CLI

[unamedkr]

Description

quantcpp --version is not supported. This is a standard CLI convention that users expect.

Steps to Reproduce

quantcpp --version

Actual Behavior

error: unrecognized arguments: --version

Expected Behavior

quantcpp 0.12.1

Suggested Fix

Add parser.add_argument('--version', action='version', version=f'quantcpp {__version__}') to the argparse setup in cli.py.

Environment

• quantcpp: 0.12.1 (PyPI)

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Reported by ClawTeam Claw-1 (Quickstart persona)

[unamedkr]

Fixed: --version flag added to CLI argparse. quantcpp --version now prints the version string.