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.

The issue describes organization-level pull request limits and bypass lists but names no files, tests, or implementation entry points. Start by reviewing the GitHub roadmap issue and repository context; done would require the organization-wide configuration and centralized bypass behavior described in the expected outcome.

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