test: increase coverage and add codecov integration

tests/setup.ts

@@ -0,0 +1,14 @@
+import { afterEach, vi } from "vitest";
+import { cleanup } from "vitest-browser-vue/pure";
+
+import { createEChartsModule } from "./helpers/mock";
+import { resetDocumentBody } from "./helpers/dom";
+
+// Mock echarts/core globally for browser tests
+vi.mock("echarts/core", () => createEChartsModule());
+
+// Centralized cleanup for all browser tests
+afterEach(() => {
+  cleanup();
+  resetDocumentBody();
+});