Give CONTRIBUTING and SECURITY a more polished layout

[Commanderx-code]

Change

Brings CONTRIBUTING.md and SECURITY.md in line with the refreshed README (#16), wiki (#17), and docs (#18).

• Both files: a centered header with a nav row (README · Docs · the other file), icons on the section headings, and GitHub callouts for the warnings and key rules.
• CONTRIBUTING:
  • The bug-report details are now a bulleted list.
  • Callouts: the "security issues go private" note (caution), the redact-your-logs note (warning), the Toolbox pointer (tip), and "report checks you couldn't run" (important).
  • The steps to contribute now have icons.
• SECURITY:
  • A prominent "Report a vulnerability privately" link in the header.
  • Callouts for "no public issues" and "latest release only".
  • The supported-versions table is centered and formatted.
  • In scope and out of scope are marked ✅/❌.

The wording is unchanged apart from those list and label tweaks. No existing links point at section anchors in these files.

Validation

• npx prettier --check CONTRIBUTING.md SECURITY.md: clean.
• npm run check: passes.

🤖 Generated with Claude Code

https://claude.ai/code/session_01BUhabxL4SPejg19jgbSyYN

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Generated by Claude Code