Add catalog item images with thumbnail preview in wizard

Each catalog item now supports one optional image (jpg/jpeg/png/gif/webp,
max 10 MB). Uploading generates a 200x200 JPEG thumbnail automatically via
SixLabors.ImageSharp. Images are stored in Azure Blob Storage under a new
catalogimages container, keyed by {companyId}/catalog/{itemId}/.

- CatalogItem entity: ImagePath + ThumbnailPath (nullable string fields)
- Migration: AddCatalogItemImages applied
- ICatalogImageService / CatalogImageService: upload, thumbnail generation,
  delete; old blobs replaced atomically on re-upload
- CatalogItemsController: Create/Edit accept optional IFormFile image;
  Image(id, thumbnail) action serves blobs with [Authorize] so wizard users
  can load thumbnails without CanManageProducts policy
- Catalog index (_CategoryNode): 40x40 thumbnail (or placeholder icon)
  left of each item name
- Details view: image card in right column with click-to-full-size link
- Create/Edit views: file picker with live preview; Edit shows current
  thumbnail with Remove checkbox
- Wizard (item-wizard.js): thumbnails in product list with hover preview
  that follows the cursor (showCatalogPreview / moveCatalogPreview);
  fixed Bootstrap d-flex !important bug that broke the filter box by
  moving flex layout to an inner wrapper div

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Application/Interfaces/ICatalogImageService.cs

@@ -0,0 +1,32 @@
+using Microsoft.AspNetCore.Http;
+
+namespace PowderCoating.Application.Interfaces;
+
+/// <summary>
+/// Handles upload, thumbnail generation, and deletion of catalog item images stored in Azure Blob Storage.
+/// All blobs are scoped under {companyId}/catalog/{itemId}/ so tenants never share a path.
+/// </summary>
+public interface ICatalogImageService
+{
+    /// <summary>
+    /// Uploads the image, generates a 200×200 JPEG thumbnail, stores both blobs, and returns their paths.
+    /// On success the caller should persist the returned paths to <c>CatalogItem.ImagePath</c> and
+    /// <c>CatalogItem.ThumbnailPath</c>.  Any previously stored blobs for the same item are deleted first.
+    /// </summary>
+    Task<(bool Success, string ImagePath, string ThumbnailPath, string ErrorMessage)> UploadAsync(
+        IFormFile file,
+        int itemId,
+        int companyId,
+        string? existingImagePath,
+        string? existingThumbnailPath);
+
+    /// <summary>
+    /// Downloads a catalog image blob and returns its raw bytes and content-type for streaming to the browser.
+    /// </summary>
+    Task<(bool Success, byte[] Content, string ContentType, string ErrorMessage)> DownloadAsync(string blobPath);
+
+    /// <summary>
+    /// Deletes both the full-size image and thumbnail blobs.  Safe to call with null paths.
+    /// </summary>
+    Task DeleteAsync(string? imagePath, string? thumbnailPath);
+}