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/totals.service.ts

@@ -9,7 +9,7 @@ export function getCategoryTotals(db: Db = prodDb) {
     .select({
       categoryId: items.categoryId,
       categoryName: categories.name,
-      categoryEmoji: categories.emoji,
+      categoryIcon: categories.icon,
       totalWeight: sql<number>`COALESCE(SUM(${items.weightGrams}), 0)`,
       totalCost: sql<number>`COALESCE(SUM(${items.priceCents}), 0)`,
       itemCount: sql<number>`COUNT(*)`,