Extend GitHub PR reviewer with independent acceptance checks

[neubig]

Desired Behavior

Extend the existing github-pr-reviewer automation to review exact PR heads using its selected profile. Reuse canonical review and QA, publish readable native reviews plus exact-head acceptance statuses, and re-review after base updates. The reviewer profile must have no GitHub code-write capability.

Acceptance Criteria

• Independently configurable automation catalog entry with its own implementation and schedule.
• Agent profile is persisted on the automation and is the source of agent settings and available secrets.
• No github-software-factory role-switched runner is required.
• Focused tests plus live validation on the existing Airbnb demo; application changes remain automation-only.
• Replace the relevant parts of feat(factory): compose canonical implementation, review, QA, and guarded merge #557/feat: run independent factory issues in bounded developer lanes #564 and document review dependencies.

[github-actions]

✅ ready-for-dev label applied

This issue meets the readiness criteria and is ready for contribution.
A contributor can now open a PR that links this issue (Fixes #<number>).

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