test(20-01): add failing tests for tag service and route

- Tag service tests: empty array, alphabetical ordering, id+name projection
- Tag route tests: GET /api/tags returns 200, correct tag objects

tests/services/tag.service.test.ts

@@ -0,0 +1,34 @@
+import { beforeEach, describe, expect, it } from "bun:test";
+import { tags } from "../../src/db/schema.ts";
+import { getAllTags } from "../../src/server/services/tag.service.ts";
+import { createTestDb } from "../helpers/db.ts";
+
+describe("Tag Service", () => {
+	let db: Awaited<ReturnType<typeof createTestDb>>["db"];
+
+	beforeEach(async () => {
+		const testDb = await createTestDb();
+		db = testDb.db;
+	});
+
+	it("returns empty array when no tags exist", async () => {
+		const result = await getAllTags(db);
+		expect(result).toEqual([]);
+	});
+
+	it("returns all tags as { id, name } ordered alphabetically", async () => {
+		await db.insert(tags).values([
+			{ name: "bikepacking" },
+			{ name: "ultralight" },
+			{ name: "accessories" },
+		]);
+
+		const result = await getAllTags(db);
+		expect(result).toHaveLength(3);
+		expect(result[0].name).toBe("accessories");
+		expect(result[1].name).toBe("bikepacking");
+		expect(result[2].name).toBe("ultralight");
+		// Should NOT include createdAt
+		expect(result[0]).toEqual({ id: expect.any(Number), name: "accessories" });
+	});
+});