fix: repair Rentman equipment sync with real API field mapping

- Map real Rentman fields: price -> rental_price, folder -> category/subcategory
  (resolved via folder hierarchy to top-level categories), code -> number,
  shop_description_long (fallback short/external_remark) -> description (HTML stripped)
- Sync only in_shop items; exclude archived/temporary from public catalog
- Extract known brands from equipment names (d&b, Shure, Pioneer, ...)
- Build specifications from physical fields (power, weight, dimensions)
- Persist equipment images in docker volume (survive redeploys)
- Router: filter available items, add price_asc/price_desc sorting
- Frontend: show prices in catalog card, detail page and cart with
  per-day subtotal; price sorting options
- Tests: use real Rentman field names in fixtures, mock folder_map

backend/app/services/sync_service.py

@@ -53,8 +53,9 @@ class SyncService:
             # Ensure images directory exists
             os.makedirs(IMAGES_DIR, exist_ok=True)
 
-            # Fetch all equipment from Rentman
+            # Fetch all equipment and folders from Rentman
             all_equipment = await self.rentman.get_all_equipment(limit=100)
+            folder_map = await self.rentman.get_folder_map()
 
             # Build set of rentman_ids from API for availability check
             api_rentman_ids = set()
@@ -75,7 +76,7 @@ class SyncService:
                     continue
 
                 try:
-                    transformed = await self.rentman.transform_equipment(raw_item)
+                    transformed = await self.rentman.transform_equipment(raw_item, folder_map=folder_map)
                     await self._upsert_equipment(transformed)
 
                     # Download image if S3 URL available