feat(pwa): add digest-ready maintainer queue notifications after research decision

[JSONbored]

Parent phase: #238
Parent roadmap: #127

Problem

Maintainer queue notifications should only ship after the mobile/PWA research decision, and they need to be digest-ready rather than noisy real-time spam.

Acceptance criteria

• Implementation is gated behind the research(mobile): validate native mobile vs PWA for maintainer digests #150 PWA/mobile research decision.
• Notifications summarize queue risk, blocked PRs, stale Gittensory output, and trust/safety issues without leaking private context.
• Users can opt in/out and understand the digest cadence.

Validation expected

• Tests cover digest content selection, opt-in/out state, and public/private redaction.
• Screenshots or recording show notification settings and digest preview if UI is touched.

UI evidence gate

Any visible web, browser-extension, or GitHub-overlay change must include maintainer-reviewable screenshots or a short recording covering the changed states. A checked template box without actual visual evidence is not enough.

Public-output safety criteria

• Public text is sanitized before reaching GitHub comments, issue bodies, PR bodies, extension-visible public panels, or copied public snippets.
• Tests cover forbidden wallet/hotkey, reward-estimate, trust-score, public-score-prediction, private-reviewability, private-scoreability, and farming-language leakage.

Cross-cutting acceptance criteria

• Preserve the repo quality gate: npm run test:ci, 97%+ global coverage, and the local branch coverage target for touched code.
• Keep public/private boundaries explicit. Public GitHub output must not expose wallets, hotkeys, reward estimates, raw trust scores, public score predictions, private reviewability, private scoreability context, or farming language.
• Add/update focused tests for the changed behavior instead of relying on green checks alone.