feat(06-01): migrate categories from emoji to Lucide icon field

- Rename emoji column to icon in schema, Zod schemas, and all services
- Add Drizzle migration with emoji-to-icon data conversion
- Update test helper, seed, and all test files for icon field
- All 87 tests pass with new icon-based schema

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

src/server/services/item.service.ts

@@ -19,7 +19,7 @@ export function getAllItems(db: Db = prodDb) {
       createdAt: items.createdAt,
       updatedAt: items.updatedAt,
       categoryName: categories.name,
-      categoryEmoji: categories.emoji,
+      categoryIcon: categories.icon,
     })
     .from(items)
     .innerJoin(categories, eq(items.categoryId, categories.id))