Add category image upload with thumbnail backdrop in category tiles

- Add category image API methods (upload/delete) to src/api/index.js
- Add uploadCategoryImage/deleteCategoryImage thunks and extraReducers in categorySlice
- Add CategoryBackdrop component showing ThumbHash placeholder with full thumb overlay
- Add photo upload/delete tab to CategoryEditTile settings cycle
- Category tile label band uses semi-transparent black overlay with white text
- Pass thumbHash/fullHash to both CategoryTile and CategoryEditTile

src/pages/artikel/kategorien.jsx

@@ -48,6 +48,8 @@ import {
   selectChildCategories,
   selectRenameMode,
   patchCategoryPosterminalIds,
+  uploadCategoryImage,
+  deleteCategoryImage,
 } from '../../store/categorySlice';
 import {
   enableTerminalCategory,
@@ -375,6 +377,33 @@ class ArtikelKategorienPage extends Component {
                   }}
                   onOpen={() => this.navigateToCategoryById(item.id)}
                   hasTerminals={hasTerminals}
+                  categoryFullHash={item.fullHash}
+                  thumbHash={item.thumbHash}
+                  onPhotoUpload={() => {
+                    const input = document.createElement('input');
+                    input.type = 'file';
+                    input.accept = 'image/*';
+                    input.onchange = async (e) => {
+                      const file = e.target.files?.[0];
+                      if (!file) return;
+                      try {
+                        // Prepare image (resize and encode to AVIF)
+                        const { prepareArticlePhoto } = await import('../../utils/prepareArticlePhoto');
+                        const avifFile = await prepareArticlePhoto(file);
+                        await this.props.uploadCategoryImage({
+                          categoryId: item.id,
+                          file: avifFile,
+                        });
+                      } catch (err) {
+                        notifyError(err);
+                      }
+                    };
+                    input.click();
+                  }}
+                  onPhotoDelete={() => {
+                    void this.props.deleteCategoryImage(item.id)
+                      .catch(notifyError);
+                  }}
                   nameInput={
                     <TextField
                       value={draftName}
@@ -417,6 +446,8 @@ class ArtikelKategorienPage extends Component {
                 key={item.id}
                 label={label}
                 onClick={() => this.navigateToCategoryById(item.id)}
+                thumbHash={item.thumbHash}
+                fullHash={item.fullHash}
               />
             );
           })}
@@ -480,6 +511,8 @@ const mapDispatchToProps = {
   enableTerminalCategory,
   disableTerminalCategory,
   patchCategoryPosterminalIds,
+  uploadCategoryImage,
+  deleteCategoryImage,
 };
 
 export default withCategoryRoute(connect(mapStateToProps, mapDispatchToProps)(ArtikelKategorienPage));