[M3] Build the pull request detail and saved queue views

[igbopharaoh]

Tracking

• Milestone: M3 - Maintainer Workflow
• Suggested labels: priority:p1, type:feature, area:api, area:web, milestone:maintainer-workflow

Context

Complete the maintainer workflow with the detail and queue experiences described by the roadmap, not only an aggregate table.

Scope

• Add a PR detail endpoint and view.
• Show triage-score components, readiness warnings, labels, linked issue/claim status, contributor context, and suggested next action.
• Add reliable views for stale-ready and large or risky pull requests.
• Link queue rows to detail while preserving repository scoping and authorization.

Acceptance criteria

• A maintainer can understand why a PR is ranked and what should happen next without reading raw events.
• Stale-ready and large/risky views are reproducible from server-side query state.
• Detail data respects installation and repository access controls.

Validation

• Exercise empty, normal, stale-ready, and high-risk UI states.

Definition of done

• Relevant Rust, API, or web tests pass.
• Documentation and runbook notes are updated when behavior changes.
• The pull request includes a concise manual verification note.