feat: modularize external providers

Tiku.Application/Notifications/INotificationProvider.cs

@@ -0,0 +1,26 @@
+using System.Text.Json;
+using Tiku.Domain.Operations;
+
+namespace Tiku.Application.Notifications;
+
+public sealed record InAppNotificationRequest(
+    Guid TenantId,
+    Guid UserId,
+    string NotificationType,
+    NotificationSeverity Severity,
+    string Title,
+    string Message,
+    Guid? CreatedBy = null,
+    string? ActionLabel = null,
+    string? ActionPath = null,
+    string? SourceType = null,
+    Guid? SourceId = null,
+    string? DedupeKey = null,
+    JsonElement Metadata = default);
+
+public interface INotificationProvider
+{
+    Task<UserNotification> UpsertInAppAsync(
+        InAppNotificationRequest request,
+        CancellationToken cancellationToken = default);
+}