Implement Notifications API with Permission Flow

[FlorianRappl]

Proposal

Add Notifications support with explicit permission handling and injected delivery backend.

Scope:

• Expose Notification constructor and static requestPermission.
• Support permission states default, granted, denied.
• Add close and basic event wiring.
  Technical Notes:
• Permission and delivery must be platform-injected.
• Integrate with Permissions API when available.
  Acceptance Criteria:
• Notification creation is blocked when permission is denied.
• requestPermission resolves through injected platform policy.
• Unit tests cover permission transitions and delivery callback invocation.
  Out of Scope:
• Native OS notification UI behavior.
• Browser-specific anti-abuse policies.

Description

Implement Notifications API basics, including Notification construction, requestPermission, and permission-state enforcement through an injected platform permission/delivery backend.

Background

Notification support is frequently needed for app parity and user-flow simulation. A platform-injected model aligns with existing Clipboard/Geolocation patterns and keeps host behavior configurable.

Specification

• Notifications specification: https://notifications.spec.whatwg.org/
• Permission model integration expected with Permissions API semantics