In-app notification transport.

Creates in-app notifications immediately (synchronous).

Behavior

1. Checks user preferences (if event is user_configurable)
2. Resolves recipients from context
3. Creates Notification records
4. Updates receipt status to :sent

Status Flow

pending → sent (success)
        ↘ failed (error)
        ↘ skipped (user opted out)

Example

receipt = %{
  content: %{
    title: "Order Created",
    message: "Your order #1234 is being processed",
    action_url: "/orders/1234",
    notification_type: :success
  }
}

InApp.deliver(receipt, context, channel, event_config)
# -> Creates Notification records
# -> Returns {:ok, updated_receipt}