Require new scripts to be submitted to ProxmoxVED (testing repo) before promotion to ProxmoxVE. Update CONTRIBUTING.md with a step-by-step workflow for adding and testing new scripts in ProxmoxVED, and clarify that bug fixes, improvements, and features for existing scripts belong in this repository. Add security vulnerability link, tighten PR guidance (small, focused PRs; CI expectations), and update README links and wording to reflect the new process.