Fix blog category selection and empty state rendering

src/TaxBaik.Web/Pages/Shared/_BlogEditor.cshtml

@@ -43,7 +43,20 @@
                     <div class="row g-3 blog-meta-grid">
                         <div class="col-md-4">
                             <label class="form-label" for="Input_CategoryId">카테고리</label>
-                            <input class="form-control" id="Input_CategoryId" name="Input.CategoryId" value="@Model.CategoryId" />
+                            <select class="form-select" id="Input_CategoryId" name="Input.CategoryId" required>
+                                @foreach (var category in (ViewData["BlogCategories"] as IEnumerable<TaxBaik.Domain.Entities.Category>) ?? [])
+                                {
+                                    if (category.Id == Model.CategoryId)
+                                    {
+                                        <option value="@category.Id" selected>@category.Name</option>
+                                    }
+                                    else
+                                    {
+                                        <option value="@category.Id">@category.Name</option>
+                                    }
+                                }
+                            </select>
+                            <span class="text-danger small" data-valmsg-for="Input.CategoryId" data-valmsg-replace="true"></span>
                         </div>
                         <div class="col-md-4">
                             <label class="form-label d-block" for="Input_IsPublished">발행 여부</label>
@@ -85,7 +98,7 @@
                     <div>
                         <div class="text-muted small text-uppercase mb-1">불러온 원본</div>
                         <div class="fw-semibold">@Model.Title</div>
-                        <div class="text-muted small">카테고리: @(Model.CategoryId?.ToString() ?? "미지정")</div>
+                        <div class="text-muted small">카테고리: @Model.CategoryId</div>
                         <div class="text-muted small">발행: @(Model.IsPublished ? "예" : "아니오")</div>
                     </div>
                     <article class="content-prose blog-preview-pane" data-blog-preview>@Html.Raw(Model.Content)</article>