Enforce unique catalog titles on creation

Added a uniqueness check for catalog titles in the creation flow. The service now prevents creating catalogs with duplicate titles by checking for existing entries before insertion. If a duplicate is detected, the API returns a 409 Conflict response. Updated interfaces and repository to support title-based lookups.

DbFirst.Infrastructure/Repositories/CatalogRepository.cs

@@ -25,6 +25,11 @@ public class CatalogRepository : ICatalogRepository
         return await _db.VwmyCatalogs.AsNoTracking().FirstOrDefaultAsync(x => x.Guid == id, cancellationToken);
     }
 
+    public async Task<VwmyCatalog?> GetByTitleAsync(string title, CancellationToken cancellationToken = default)
+    {
+        return await _db.VwmyCatalogs.AsNoTracking().FirstOrDefaultAsync(x => x.CatTitle == title, cancellationToken);
+    }
+
     public async Task<VwmyCatalog> InsertAsync(VwmyCatalog catalog, CancellationToken cancellationToken = default)
     {
         var guidParam = new SqlParameter("@GUID", SqlDbType.Int)