Add validator environment doctor

[ZhiHe-ma]

Summary

• Add a zero-dependency environment doctor for the JSON validator CLIs.
• Report the Node.js version, OS, architecture, and whether O_NOFOLLOW and O_NONBLOCK are non-zero integers, matching the validators' current rule.
• Provide human-readable, stable JSON, and help output with exit codes 0 (ready/help), 1 (missing capability), and 2 (invalid arguments).
• Document the narrow scope and recommend Linux/WSL when protected file-opening flags are unavailable.

Usage

node skills/security-audit/check-environment.cjs
node skills/security-audit/check-environment.cjs --json
node skills/security-audit/check-environment.cjs --help

The result covers only the JSON validators' file-reading prerequisites. It does not claim that the complete audit environment or an OS-enforced security sandbox has been verified, and it does not impose a minimum Node.js version.

Testing

• node --test skills/security-audit/check-environment.test.cjs: 14 passed, 0 failed, 0 skipped on Node.js v24.19.0 / win32 / x64.
• Real CLI text, JSON, help, and invalid-argument invocations were exercised. Native Windows correctly returned 1 because Node.js does not expose either required flag there.
• Existing validator suites: 46 passed, 7 failed, 12 skipped. The same 7 findings-CLI tests fail on an unmodified archive of origin/main at c1c8a8c1471069fb0e188eeaff69b8e8db6564a8, all because the protected file-opening flags are unavailable on native Windows. This PR does not alter those tests or validators.
• Documentation commands were run and git diff --check passed.

Pre-PR overlap and conflict check

Immediately before opening this PR, I refreshed origin/main and related open PR heads. None added these paths or an equivalent doctor command. git merge-tree --write-tree reported no text conflicts with main or PRs #25, #26, #31, #33, #34, #36, #38, #44, and #48 at their then-current heads.