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>

tests/services/totals.test.ts

@@ -16,7 +16,7 @@ describe("Totals Service", () => {
 
   describe("getCategoryTotals", () => {
     it("returns weight sum, cost sum, item count per category", () => {
-      const shelter = createCategory(db, { name: "Shelter", emoji: "\u{26FA}" });
+      const shelter = createCategory(db, { name: "Shelter", icon: "tent" });
       createItem(db, {
         name: "Tent",
         weightGrams: 1200,
@@ -39,7 +39,7 @@ describe("Totals Service", () => {
     });
 
     it("excludes empty categories (no items)", () => {
-      createCategory(db, { name: "Shelter", emoji: "\u{26FA}" });
+      createCategory(db, { name: "Shelter", icon: "tent" });
       // No items added
       const totals = getCategoryTotals(db);
       expect(totals).toHaveLength(0);