feat(backend): add communication, tester, admin and middleman modules

Implement step 17 modules: threads/messages, notifications with automation (submission.created, idea.created, grant_call.opened), innovation test feedback, admin panel (submissions, verify, metrics, grant call status), Middleman adaptation and partnerships. Split multi-type files into one type per file and replace object-valued dictionaries with string-valued maps in data contracts (migrations 0006/0007).

backend/Application/Abstractions/INotificationService.cs

@@ -0,0 +1,27 @@
+using TarninaHub.Application.Dtos;
+
+namespace TarninaHub.Application.Abstractions;
+
+
+public interface INotificationService
+{
+    Task NotifyStaffAsync(
+        string type,
+        IReadOnlyDictionary<string, string?> payload,
+        CancellationToken cancellationToken);
+
+    Task NotifyUserAsync(
+        string userId,
+        string type,
+        IReadOnlyDictionary<string, string?> payload,
+        CancellationToken cancellationToken);
+
+    Task<IReadOnlyList<NotificationResponse>> ListForUserAsync(
+        string userId,
+        CancellationToken cancellationToken);
+
+    Task<NotificationResponse?> MarkReadAsync(
+        string notificationId,
+        string userId,
+        CancellationToken cancellationToken);
+}