feat(notifications): event-to-subscription-to-delivery service

[JSONbored]

Parent roadmap: #525
Parent phase: #527

Background

When a reviewer requests changes on a miner's PR, the miner is never told by Gittensory — so fixes are slow and merge rates suffer. Closing this loop is the wave's killer use case. This issue absorbs #255 (digest notifications) but decouples the miner real-time alert from the #150 PWA research gate by shipping it on the extension badge channel first.

Goal

A new event → subscription → delivery notifications service on the existing JOBS queue.

Current Behavior

pull_request_review webhooks are received but the author is never notified; there is no notification service and no review field on the payload (see #527 review-field child).

Desired Behavior

• Add notify-evaluate / notify-deliver job types to the JobMessage union + processJob switch (src/queue/processors.ts). Emit events from detectNotificationEvents inside processGitHubWebhook.
• Killer event: pull_request_review state changes_requested → alert the author. Other events: PR going stale, duplicate cluster forming, new high-fit issue; maintainer-side gate failure / SLA breach (cron-driven).
• Channels sequenced: extension badge (pull-based, ships with the rebuild) + email → PWA web push → Slack/Discord.

Implementation Requirements

• New D1 tables mirroring digest_subscriptions with a UNIQUE(dedup_key, channel) idempotency guard + per-recipient rate-limit. changes_requested delivers immediately; chatty events coalesce. Depends on the review-field child (roadmap(pillar 2): surfaces — browser-extension rebuild & notifications #527).

Public/Private Output Boundaries

• Templated, public-safe copy only; payloads carry { repo, pr, eventType, deeplink }. Suppress self-notifications and bot loops.

Acceptance Criteria

• A changes_requested review produces exactly one delivery (idempotent) end-to-end via the badge channel, not gated behind research(mobile): validate native mobile vs PWA for maintainer digests #150.

Testing Requirements

• npm run test:ci, 97%+ coverage. Idempotency test (duplicate webhook/queue retry → one delivery); self-notification suppression; rate-limit window.

Sub-issues

• feat(notifications): event detection (changes-requested) #566 event detection (changes-requested)
• feat(notifications): D1 data model + idempotency guard #567 D1 data model + idempotency
• feat(notifications): queue jobs (notify-evaluate/deliver) #568 queue jobs (notify-evaluate/deliver)
• feat(notifications): extension-badge delivery channel #569 extension-badge delivery
• feat(notifications): email delivery channel #570 email delivery

Wave 3 refinement (#525)

This issue already owns the killer event (changes_requested → alert the author). Refinements: the alert should carry the predicted-gate delta + concrete fix list (reuse the #688 predicted-gate engine), and also fire on merge to feed #702 (miner reward attribution). #699 (issue-watch) is the new-issue half of the same miner feed.