fix(cli): handle top-level version flag

[vsolano9]

What & why

Handle --version before the missing-command usage branch so a conventional top-level version probe prints the CLI version and exits successfully. This keeps install and CI version probes from being treated as usage errors.

Closes #4

Changes

• prioritize --version before bare-invocation usage handling
• assert --version prints only a semantic version and returns 0
• pin neighboring bare invocation (exit 2) and explicit help (exit 0) behavior

Validation

• npm test — 7 files, 53 tests passed
• npm run lint
• npm run typecheck
• npm run build
• focused CLI test repeated 20 times
• full tests and TypeScript build under Node 20.20.2 and Node 22.23.2
• git diff --check

Checklist

• focused change with regression coverage
• documented repository checks pass
• no dependency or configuration changes
• linked issue with Closes #4

[github-actions]

Welcome, @vsolano9, and thanks for your first pull request to MCP-audit.

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I'll review this shortly. Ask anything in the thread if something is unclear.