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/Dtos/NotificationResponse.cs

@@ -0,0 +1,11 @@
+using System.ComponentModel.DataAnnotations;
+
+namespace TarninaHub.Application.Dtos;
+
+
+public sealed record NotificationResponse(
+    string Id,
+    string Type,
+    IReadOnlyDictionary<string, string?> Payload,
+    DateTimeOffset? ReadAt,
+    DateTimeOffset CreatedAt);