docs: add CONTRIBUTING.md and SECURITY.md

[shenxianpeng]

Add missing community health files required for opensoruce compliance.

• CONTRIBUTING.md — Setup instructions, test commands, code style, and PR process
• SECURITY.md — Private vulnerability reporting policy and supported versions

Both files are kept intentionally short and focused.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 74d53687-8984-469b-94f4-7e4b14c5565d

📥 Commits

Reviewing files that changed from the base of the PR and between 4296446 and 2e9ed3c.

📒 Files selected for processing (2)

• CONTRIBUTING.md
• SECURITY.md

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch chore/add-contributing-and-security

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.07%. Comparing base (4296446) to head (2e9ed3c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #235   +/-   ##
=======================================
  Coverage   97.07%   97.07%           
=======================================
  Files           4        4           
  Lines         239      239           
=======================================
  Hits          232      232           
  Misses          7        7           

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