Add SECURITY.md (RSR compliance)

Author: hyperpolymath

SECURITY.md

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+# Security Policy
+
+## Reporting a Vulnerability
+
+If you discover a security vulnerability, please report it responsibly:
+
+1. **Do not** open a public issue
+2. Email security concerns to the maintainer
+3. Include steps to reproduce the vulnerability
+4. Allow reasonable time for a fix before disclosure
+
+## Supported Versions
+
+| Version | Supported          |
+| ------- | ------------------ |
+| latest  | :white_check_mark: |
+| < latest| Best effort        |
+
+## Security Updates
+
+Security patches are released as soon as possible after verification.
+