Add user-specific persistent grid/band layouts support

Implemented user-customizable, persistent grid and band layouts for CatalogsGrid and MassDataGrid. Added backend API, database entity, and repository for storing layouts per user. Refactored grids to support dynamic band/column rendering, layout management UI, and per-user storage via localStorage and the new API. Registered all necessary services and updated data context. Enables flexible, user-specific grid experiences with saved layouts.

DbFirst.BlazorWebApp/Services/LayoutApiClient.cs

@@ -0,0 +1,64 @@
+using System.Net.Http.Json;
+using DbFirst.BlazorWebApp.Models;
+
+namespace DbFirst.BlazorWebApp.Services;
+
+public class LayoutApiClient
+{
+    private readonly HttpClient _httpClient;
+    private const string Endpoint = "api/layouts";
+
+    public LayoutApiClient(HttpClient httpClient)
+    {
+        _httpClient = httpClient;
+    }
+
+    public async Task<LayoutDto?> GetAsync(string layoutType, string layoutKey, string userName)
+    {
+        var url = $"{Endpoint}?layoutType={Uri.EscapeDataString(layoutType)}&layoutKey={Uri.EscapeDataString(layoutKey)}&userName={Uri.EscapeDataString(userName)}";
+        var response = await _httpClient.GetAsync(url);
+        if (response.StatusCode == System.Net.HttpStatusCode.NotFound)
+        {
+            return null;
+        }
+
+        response.EnsureSuccessStatusCode();
+        return await response.Content.ReadFromJsonAsync<LayoutDto>();
+    }
+
+    public async Task<LayoutDto> UpsertAsync(LayoutDto dto)
+    {
+        var response = await _httpClient.PostAsJsonAsync(Endpoint, dto);
+        if (!response.IsSuccessStatusCode)
+        {
+            var detail = await ReadErrorAsync(response);
+            throw new InvalidOperationException(detail);
+        }
+
+        var payload = await response.Content.ReadFromJsonAsync<LayoutDto>();
+        return payload ?? dto;
+    }
+
+    private static async Task<string> ReadErrorAsync(HttpResponseMessage response)
+    {
+        var body = await response.Content.ReadAsStringAsync();
+        if (!string.IsNullOrWhiteSpace(body))
+        {
+            return body;
+        }
+
+        return $"{(int)response.StatusCode} {response.ReasonPhrase}".Trim();
+    }
+
+    public async Task DeleteAsync(string layoutType, string layoutKey, string userName)
+    {
+        var url = $"{Endpoint}?layoutType={Uri.EscapeDataString(layoutType)}&layoutKey={Uri.EscapeDataString(layoutKey)}&userName={Uri.EscapeDataString(userName)}";
+        var response = await _httpClient.DeleteAsync(url);
+        if (response.StatusCode == System.Net.HttpStatusCode.NotFound)
+        {
+            return;
+        }
+
+        response.EnsureSuccessStatusCode();
+    }
+}