feat(17-03): update client components to use imageUrl from API responses

- Replace all /uploads/ path construction with imageUrl presigned URLs
- Add imageUrl prop to ItemCard, CandidateCard, CandidateListItem, ComparisonTable
- Update ImageUpload to use presigned URLs + local preview for new uploads
- Pass imageUrl through from parent components (CollectionView, forms, routes)

src/client/routes/threads/$threadId.tsx

@@ -275,6 +275,7 @@ function ThreadDetailPage() {
 							categoryName={candidate.categoryName}
 							categoryIcon={candidate.categoryIcon}
 							imageFilename={candidate.imageFilename}
+							imageUrl={candidate.imageUrl}
 							productUrl={candidate.productUrl}
 							threadId={threadId}
 							isActive={isActive}