Document Release Engineering Team policies

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Summary

Add releng/policies.adoc documenting policies for release schedule,
content decisions, commit access, code freezes, and support lifecycle.
Covers major and minor release policies, branch management, and
support timelines (4 years branch, 3 years releases).

Update releng/_index.adoc to link to new charter and policies
documents.

Co-Authored-By: Claude Haiku 4.5 <[e-mail]>

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Move to handbook

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documentation/content/en/books/developers-handbook/policies/releng.adoc

10–12

Should this be encoded here, or should it just indicate that the RE lead / team is responsible for determining and publishing the release schedule?

26

This list doesn't really match what we do today, although following this would be my preference.

Should add "New hardware support in existing drivers" though (new PCI IDs for instance)

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documentation/content/en/books/developers-handbook/policies/releng.adoc

10–12

It's what we document elsewhere, though we should change it to at least mention the release cadence stuff since that removes some discretion.

Though to be honest, this is also a bit a straw-man to fill in the gaps and make sure there's a shared understanding...

26

This list doesn't really match what we do today, although following this would be my preference.

Should add "New hardware support in existing drivers" though (new PCI IDs for instance)

Yes. Add new hardware support generally for existing drivers is a bit more expansive. We want things to be between these two poles (more towards just adding PCI IDs), but there's always a pragmatic angle that people want to run new hardware with older, but still supported branches.