Revise security policy and reporting guidelines

Updated the security policy to clarify reporting procedures and supported versions.

Author: matzefriedrich

SECURITY.md

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+# Security Policy
+
+This project is provided as source code only and intended for technical users who build it themselves. No binaries are distributed.
+
+## Reporting a Vulnerability
+
+If you believe you’ve found a security issue, **do not disclose any details in public issues or pull requests**.
+
+Please report potential security problems **exclusively via email**:
+
+**security contact:** *[email protected]*
+
+If you accidentally opened a public issue first, remove all details and leave a brief note, such as: “Security report sent via email.”*
+
+## Scope
+
+Only issues that affect the **latest (pre-)release** or the current `main` branch will be investigated. If the problem does not exist in the newest version, it will not be reviewed or addressed.