Public project launch preparation

[alyldas]

What changed

• Updated the organization profile from private pre-release wording to public pre-1.0 status.
• Expanded the shared contribution guide for package and ecosystem repositories.
• Updated support and security routes for the now-public repository set.
• Aligned the bug template with PostgreSQL 18.
• Hardened the community-file workflow with a timeout and credential-free checkout.

Why

The package and central repositories are now public. The inherited community files must describe the actual contribution, support, and vulnerability-reporting model before the first package release.

Impact

Repository code and package behavior are unchanged. Contributors receive consistent organization-wide guidance, and security reports are routed through private vulnerability reporting.

Checks

• Required community files are present and non-empty.
• Workflow and issue-template YAML parse successfully.
• Git diff whitespace validation passes.