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/useThreads.ts

@@ -8,7 +8,7 @@ interface ThreadListItem {
   resolvedCandidateId: number | null;
   categoryId: number;
   categoryName: string;
-  categoryEmoji: string;
+  categoryIcon: string;
   createdAt: string;
   updatedAt: string;
   candidateCount: number;
@@ -29,7 +29,7 @@ interface CandidateWithCategory {
   createdAt: string;
   updatedAt: string;
   categoryName: string;
-  categoryEmoji: string;
+  categoryIcon: string;
 }
 
 interface ThreadWithCandidates {