feat(06-03): update display components to use categoryIcon with LucideIcon

- Rename categoryEmoji to categoryIcon in ItemCard, CandidateCard, ThreadCard, ItemPicker
- Import and render LucideIcon at appropriate sizes (36px placeholder, 14-16px badges)
- Update hook interfaces to match server API (categoryIcon instead of categoryEmoji)
- Rename iconData.ts to iconData.tsx (contains JSX)
- Update useCategories mutation type to use icon instead of emoji

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/client/hooks/useCategories.ts

@@ -29,7 +29,7 @@ export function useUpdateCategory() {
     }: {
       id: number;
       name?: string;
-      emoji?: string;
+      icon?: string;
     }) => apiPut<Category>(`/api/categories/${id}`, data),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ["categories"] });