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/store/categorySlice.js

@@ -238,6 +238,38 @@ export const toggleCategoryPos = createAsyncThunk(
   },
 );
 
+/**
+ * POST /api/category/:id/image → 201 { category: { id, fullHash, thumbW, thumbH, thumbHash } }
+ */
+export const uploadCategoryImage = createAsyncThunk(
+  'category/uploadImage',
+  async ({ categoryId, file }, { rejectWithValue }) => {
+    try {
+      const data = await category.uploadImage(categoryId, file);
+      requireObject(data.category, 'POST /api/category/:id/image');
+      return data.category;
+    } catch (err) {
+      return catchBackendError(rejectWithValue)(err);
+    }
+  },
+);
+
+/**
+ * DELETE /api/category/:id/image → 200 { category: { id, thumbW: null, thumbH: null, thumbHash: null } }
+ */
+export const deleteCategoryImage = createAsyncThunk(
+  'category/deleteImage',
+  async (categoryId, { rejectWithValue }) => {
+    try {
+      const data = await category.deleteImage(categoryId);
+      requireObject(data.category, 'DELETE /api/category/:id/image');
+      return data.category;
+    } catch (err) {
+      return catchBackendError(rejectWithValue)(err);
+    }
+  },
+);
+
 const initialState = {
   companyId: null,
   languageId: null,
@@ -442,6 +474,30 @@ const categorySlice = createSlice({
           state.categories[key] = { ...existing, pos: updated.pos };
         }
       })
+      .addCase(uploadCategoryImage.fulfilled, (state, action) => {
+        const { id, fullHash, thumbW, thumbH, thumbHash } = action.payload;
+        if (id == null || state.categories == null) return;
+        const key = String(id);
+        const existing = state.categories[key];
+        if (existing) {
+          state.categories[key] = { ...existing, fullHash, thumbW, thumbH, thumbHash };
+        }
+      })
+      .addCase(deleteCategoryImage.fulfilled, (state, action) => {
+        const { id } = action.payload;
+        if (id == null || state.categories == null) return;
+        const key = String(id);
+        const existing = state.categories[key];
+        if (existing) {
+          state.categories[key] = {
+            ...existing,
+            fullHash: null,
+            thumbW: null,
+            thumbH: null,
+            thumbHash: null,
+          };
+        }
+      })
       .addCase(loadCurrentCompany.fulfilled, (state, action) => {
         const nextCompanyId = action.payload?.id ?? null;
         if (nextCompanyId != null && nextCompanyId !== state.companyId) {