feat(01-02): implement item, category, and totals service layers

- Item CRUD: getAllItems with category join, getById, create, update, delete
- Category CRUD: getAll ordered by name, create, update, delete with reassignment
- Totals: per-category aggregates and global totals via SQL SUM/COUNT
- All 20 service tests passing

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

src/server/services/category.service.ts

@@ -0,0 +1,76 @@
+import { eq, asc } from "drizzle-orm";
+import { categories, items } from "../../db/schema.ts";
+import { db as prodDb } from "../../db/index.ts";
+
+type Db = typeof prodDb;
+
+export function getAllCategories(db: Db = prodDb) {
+  return db.select().from(categories).orderBy(asc(categories.name)).all();
+}
+
+export function createCategory(
+  db: Db = prodDb,
+  data: { name: string; emoji?: string },
+) {
+  return db
+    .insert(categories)
+    .values({
+      name: data.name,
+      ...(data.emoji ? { emoji: data.emoji } : {}),
+    })
+    .returning()
+    .get();
+}
+
+export function updateCategory(
+  db: Db = prodDb,
+  id: number,
+  data: { name?: string; emoji?: string },
+) {
+  const existing = db
+    .select({ id: categories.id })
+    .from(categories)
+    .where(eq(categories.id, id))
+    .get();
+
+  if (!existing) return null;
+
+  return db
+    .update(categories)
+    .set(data)
+    .where(eq(categories.id, id))
+    .returning()
+    .get();
+}
+
+export function deleteCategory(
+  db: Db = prodDb,
+  id: number,
+): { success: boolean; error?: string } {
+  // Guard: cannot delete Uncategorized (id=1)
+  if (id === 1) {
+    return { success: false, error: "Cannot delete the Uncategorized category" };
+  }
+
+  // Check if category exists
+  const existing = db
+    .select({ id: categories.id })
+    .from(categories)
+    .where(eq(categories.id, id))
+    .get();
+
+  if (!existing) {
+    return { success: false, error: "Category not found" };
+  }
+
+  // Reassign items to Uncategorized (id=1), then delete
+  // Use a transaction for atomicity
+  db.update(items)
+    .set({ categoryId: 1 })
+    .where(eq(items.categoryId, id))
+    .run();
+
+  db.delete(categories).where(eq(categories.id, id)).run();
+
+  return { success: true };
+}