🔧 Repository: process for offboarding inactive codeowners

### 📜 Description

Some CODEOWNERS have become inactive over time, which can unintentionally create blockers in reviews and workflows. While we’re very grateful for everyone’s past contributions and continued support, we need a clear and respectful process for managing inactivity and offboarding inactive codeowners.

The [Plugin Maintainers Guide](https://github.com/backstage/community-plugins/blob/main/docs/plugin-maintainers-guide.md#stepping-down-as-a-plugin-owner) already outlines a respectful process for stepping down as a plugin owner, and we should align with that.

Building on that, the agreed [Backstage Governance](https://github.com/backstage/community/blob/main/GOVERNANCE.md#inactivity) provides additional guidance on inactivity:

> Inactivity is measured by periods of no contributions without explanation, for
> longer than:
>
> - Core Maintainer: 2 months
> - Project Area Maintainer: 4 months
> - Plugin Maintainer: 6 months
> - Organization Member: 12 months
>
> Consequences of being inactive include:
>
> - Involuntary removal or demotion
> - Being asked to move to Emeritus status

Since the Backstage GOVERNANCE already defines the six-month threshold, I think any deviation from that should be a separate discussion.

While some guidance exists, I believe we need a process to start identifying inactive contributors and reaching out to ask whether they’d like to consider moving to emeritus status. I do have some scripts on a branch that can help check activity levels we could build on.

Start with the Plugin Maintainers Guide’s stepping-down section and the inactivity section of GOVERNANCE.md, then review the existing activity-checking scripts mentioned in the issue. Done means documenting a respectful offboarding and emeritus process for inactive CODEOWNERS that aligns with the existing six-month threshold.

Written by the indexing model from the issue text.