Add Notifications module (multi-channel: mail / db / SMS / Slack / push)

[antosubash]

Background

SimpleModule has an Email module but no abstraction over notification channels. Laravel's Notification class lets a single notification flow across mail, database, broadcast, SMS, Slack, push, etc., with per-recipient channel routing. This is high-leverage: every other module (Users password reset, Orders confirmation, Admin alerts, BackgroundJobs failures) becomes a consumer.

Motivation

• One API to send across many channels
• Per-user opt-in/out per channel (stored in Settings)
• The database channel powers the in-app bell-icon UI (mark-as-read, unread count)
• Decouples what to send from how to send

Design sketch

New module modules/Notifications (Contracts + Impl + Tests):

public interface INotification
{
 string[] Via(IUser user); // ["mail", "database", "slack"]
 MailMessage? ToMail(IUser user) => null;
 object? ToDatabase(IUser user) => null;
 SlackMessage? ToSlack(IUser user) => null;
 SmsMessage? ToSms(IUser user) => null;
}

public interface INotifier
{
 Task SendAsync<T>(IUser user, T notification, CancellationToken ct = default) where T : INotification;
 Task SendNowAsync<T>(IUser user, T notification, CancellationToken ct = default) where T : INotification;
}

public interface INotificationChannel
{
 string Name { get; }
 Task SendAsync(IUser user, INotification notification, CancellationToken ct);
}

• Channels shipped: MailChannel (uses Email module), DatabaseChannel (persists Notification { Id, UserId, Type, Data (json), ReadAt, CreatedAt })
• Optional channels (separate packages): SlackChannel, WebPushChannel, SmsChannel
• Async dispatch goes through BackgroundJobs; SendNowAsync is synchronous
• Settings entries per channel: Notifications.Channel.{Name}.Enabled (per-user override)
• Inertia bell-icon component in admin shell consumes /api/notifications (list/unread-count/mark-read endpoints)

Acceptance criteria

• modules/Notifications scaffolded via sm new module Notifications and follows Constitution
• INotifier resolvable from any module via DI
• Mail + Database channels in-tree
• In-app bell-icon UI with unread count, mark-as-read, and pagination
• User preferences stored in Settings
• xUnit tests for each channel + integration test for end-to-end Send
• NBomber load-test scenario Notifications_Send
• Docs page under /docs

References

• Laravel Notifications: https://laravel.com/docs/notifications
• Existing Email module: modules/Email