Add Noxen to Security Tools

[ps-snyman]

Adds Noxen to the Security Tools section.

• What: Noxen is a Mac-native vulnerability scanner for SSH-managed Linux fleets. Agentless CVE matching against a signed daily feed, exposed-admin-surface detection (~70 services), TLS auditing, and scheduled background scans.
• Homepage: https://noxen.app/
• Distribution: Notarised Developer ID direct download (Sparkle auto-update), universal binary (Apple Silicon + Intel), macOS 26+. 14-day full-feature trial; permanent free tier covers 3 hosts.
• Why this list: Fits alongside existing entries like Mana Security and Vulert in the same section — Mac-native, security-focused, end-user app.

Compliance with docs/CONTRIBUTING.md

• Searched for duplicates — no existing Noxen entry. (Note: there is an unrelated NoxKey app already listed; different product.)
• Title-cased name format: [Noxen](https://noxen.app/).
• Added in alphabetical position within Security Tools section (between Mana Security and OverSight in en, ja; near MalwareBytes in zh, ko which are partial translations).
• Single sentence description, ≤ existing-entry length.
• Synced across all four READMEs: README.md, README-zh.md, README-ja.md, README-ko.md, with translated descriptions (best-effort — happy to revise if the maintainer's \$awesome-mac-maintainer skill produces preferred phrasing).
• No trailing whitespace; diff is 4 lines (one per README).

Disclosure

Author submission. AI-assisted contribution (Claude) per the AI-assisted contributions section of CONTRIBUTING.md — followed the repository's category, ordering, wording, and multilingual sync rules manually rather than via the Codex skill.