Add Push API Core (PushManager and Subscriptions)

[FlorianRappl]

Proposal

Provide Push API primitives for subscription lifecycle and payload delivery wiring.

Scope:

• Expose PushManager on service worker registration.
• Implement subscribe, getSubscription, and unsubscribe.
• Model PushSubscription shape and endpoint/keys data.
  Technical Notes:
• Use injected push transport backend.
• Integrate with Notifications and Permissions constraints.
  Acceptance Criteria:
• Subscriptions are origin-scoped and retrievable.
• Unsubscribe removes active subscription state.
• Tests cover permission-denied and backend failure paths.
  Out of Scope:
• Real vendor push service integration by default.
• Full encrypted payload stack in first pass.

Description

Add Push API core primitives: PushManager access on service worker registration, subscribe/getSubscription/unsubscribe, and subscription object modeling.

Background

Push is central to modern engagement workflows and service-worker-driven messaging. A minimal subscription lifecycle is sufficient for many test and integration scenarios.

Specification

• Push API specification: https://w3c.github.io/push-api/
• Integration expectations with Notifications and permissions