Refactor message service and move tests to Application.Tests

Renamed IMessageService to IMessageCommandService and updated all usages accordingly. Moved and renamed test files from Govor.API.Tests to the new Govor.Application.Tests project, updating namespaces to match. Refactored message-related services and controllers to use the new naming and structure. Added Govor.Application.Tests project to the solution.

Govor.Application/Infrastructure/AdminsStuff/InvitationGenerator.cs

@@ -0,0 +1,26 @@
+using Govor.API.Services.AdminsStuff.Interfaces;
+using Govor.Core.Models;
+using Govor.Core.Repositories.Invaites;
+
+namespace Govor.Application.Infrastructure.AdminsStuff;
+
+public class InvitationGenerator(IInvitesRepository repository) : IInvitationGenerator
+{
+    public async Task<string> GenerateInvitationCode(DateTime time, int maxUsers, bool isAdmin, string description = "")
+    {
+        Invitation newInvitation = new Invitation()
+        {
+            Id = Guid.NewGuid(),
+            Description = description,
+            MaxParticipants = maxUsers,
+            DateCreated = DateTime.UtcNow,
+            EndDate = time.ToUniversalTime(),
+            Code = Guid.NewGuid().ToString("N"),
+            IsAdmin = isAdmin
+        };
+
+       await repository.AddAsync(newInvitation);
+        
+        return newInvitation.Code;
+    }
+}