Adopt C# 12 collection expressions for empty lists/dicts

Refactored code to use C# 12 collection expressions ([]) for initializing empty lists and dictionaries instead of the older constructors. This change modernizes and simplifies collection initialization across models, services, and API clients without altering any logic.

DbFirst.BlazorWebApp/Services/CatalogApiClient.cs

@@ -17,7 +17,7 @@ public class CatalogApiClient : ICatalogApiClient
     public async Task<List<CatalogReadDto>> GetAllAsync(CancellationToken ct = default)
     {
         var result = await _httpClient.GetFromJsonAsync<List<CatalogReadDto>>(Endpoint, ct);
-        return result ?? new List<CatalogReadDto>();
+        return result ?? [];
     }
 
     public async Task<CatalogReadDto?> GetByIdAsync(int id, CancellationToken ct = default)