feat: add diagnostic version check command to CLI

[arcgod-design]

Summary

• Adds --version / -V flag to print version, Python, and platform info, then exit
• Adds �ersion subcommand with a rich diagnostics table (version, Python, platform, executable, package location)
• Adds 4 tests in ests/test_cli_version.py

Changes

• �gentwatch/cli/main.py: Add --version option to main_callback, add �ersion subcommand
• ests/test_cli_version.py: New test file with 4 tests

Testing

All 4 tests pass:

• \ est_version_flag_outputs_version\
• \ est_version_subcommand_outputs_version\
• \ est_version_subcommand_shows_python\
• \ est_version_subcommand_shows_platform\

Closes

closes #149

[sreerevanth]

fix ci

[github-actions]

🧪 PR Test Results

Check	Result
Tests (pytest tests/)	✅ success
Lint (ruff check .)	❌ failure
Coverage (agentwatch)	73.32%

_{Python 3.12 · commit 7b15dcc}