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.Web/Views/Help/Quotes.cshtml

@@ -123,6 +123,23 @@
                 </div>
             </div>
 
+            <h3 class="h6 fw-semibold mt-3 mb-2">Selecting a Product from Catalog</h3>
+            <p>
+                When you choose the <strong>Product from Catalog</strong> item type, the wizard shows a scrollable
+                list of all your active catalog items with a search box at the top. Start typing any part of the
+                item name, SKU, or category to filter the list instantly.
+            </p>
+            <p>
+                If an image has been uploaded for a catalog item, a small thumbnail appears to the left of its
+                name in the list. <strong>Hover over the thumbnail</strong> to see a larger preview near your
+                cursor — useful for quickly confirming you have the right part without opening the full item record.
+            </p>
+            <p>
+                Images are managed on the <a href="/CatalogItems">Catalog Items</a> page — open any item, click
+                <strong>Edit</strong>, and use the <strong>Item Image</strong> section to upload a photo
+                (jpg, jpeg, png, gif, or webp; max 10 MB). A 200&times;200 thumbnail is generated automatically.
+            </p>
+
             <h3 class="h6 fw-semibold mt-3 mb-2">Coatings and Prep Services</h3>
             <p>
                 For Calculated and AI Photo items, after entering the surface area you proceed to the coatings