message_pusher 1.0.0-alpha1

Adds a message_notify Notifier plugin (id: pusher) that delivers Message
entities over Pusher / Soketi / pws via the pusher_api module.

Features:
- Channel pattern with token substitution: {uid}, {template},
{linked_entity_type}, {linked_entity_id}.
- Multiple channels per send via additional_channels config.
- Token-driven access() — broadcast channels work for owner-less
Messages, private-user.{uid} requires a recipient, etc.
- Optional rendered HTML in payload (off by default).
- Kernel test coverage for happy path, failure path, access scoping,
token resolution, multi-channel fan-out.

Use cases: notifications, activity streams, chat, live dashboards,
broadcasts — anything that fits the Message entity shape.