Add ability to set PR limits at an org level [GA]

### Value Prop
You can now set pull request limits across an entire organization from a single place, rather than configuring each repository individually. Org-level bypass lists let you manage trusted contributors centrally, so the right people always have access without repeating that work repo by repo. This makes it practical to enforce consistent contribution policies at scale, even across organizations with hundreds of repositories.

### Expected Outcome
Teams managing large numbers of repositories gain meaningful time back by configuring PR limits once at the org level instead of touching every repo. Central bypass list management reduces the risk of inconsistent trust settings slipping through the cracks. The result is a more reliable and maintainable workflow for maintainers who need to govern open source or enterprise contribution policies at scale.

该 issue 描述了组织级 pull request 限制和绕过列表，但没有指出任何文件、测试或实现入口。首先查看 GitHub roadmap issue 和 repository 上下文；完成标准是实现预期结果中所描述的组织范围配置和集中式绕过行为。

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