refactor: replace Reliability Inbox ratings with evidence

[oleiade]

Summary

• removes the High value, High confidence, numbered priority, and Ready to review labels
• presents one review-order cue alongside the observable coverage and traffic evidence
• treats confidence as an eligibility gate for missing coverage and orders eligible recommendations by technical relevance
• removes generated business-value rationale because the product only has technical signals

Why

Every item in the Reliability Inbox is intended to be actionable, while the system cannot determine business criticality. Ratings therefore duplicated the queue ordering and asked users to trust unsupported judgments. This change shows what was observed and what coverage matching found instead.

User impact

Users see a simpler review queue with “Recommended next,” “No matching check found,” and recent traffic evidence. The detail view explains that no matching Synthetic Monitoring check was found and keeps the existing “How we checked” limitations. Suggestions without high confidence in missing coverage are not surfaced.

Validation

• yarn test src/features/reliabilityInbox/ReliabilityInboxPage.test.tsx src/features/reliabilityInbox/model.test.ts src/features/reliabilityInbox/ReliabilityInboxBanner.test.tsx --runInBand
• yarn typecheck
• yarn lint (passes with 13 pre-existing no-console warnings)
• yarn build

Stacked on #1773.