feat(settings): define focus-manifest policy schema

[JSONbored]

Parent roadmap: #127
Parent phase: #236
Parent epic: #277
Related advanced phase: #269

Goal

Define the normalized policy schema produced from repo focus manifests before wiring downstream owner or maintainer workflows.

Requirements

• Specify fields for contribution lanes, discouraged work, label expectations, validation expectations, and readiness warnings.
• Keep schema output deterministic and machine-readable.
• Do not implement onboarding-pack or UI integration in this issue.

Acceptance criteria

• Focus manifest policy output has a tested schema.
• Public-safe fields are separated from private/authenticated fields.
• Schema language avoids reward estimates, public scoring, wallet, hotkey, raw trust, private scoreability, and private reviewability.
• This is not an autonomous PR bot.

Validation expected

• Schema fixture tests for minimal, typical, and missing-field manifests.
• Public/private sanitizer tests.
• npm run test:ci.