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/components/CandidateForm.tsx

@@ -142,6 +142,11 @@ export function CandidateForm({
 			{/* Image */}
 			<ImageUpload
 				value={form.imageFilename}
+				imageUrl={
+					mode === "edit" && candidateId != null
+						? thread?.candidates?.find((c) => c.id === candidateId)?.imageUrl
+						: null
+				}
 				onChange={(filename) =>
 					setForm((f) => ({ ...f, imageFilename: filename }))
 				}