refactor: theme manager (#17976)

web/src/test-data/setup.ts

@@ -4,3 +4,15 @@ import { init } from 'svelte-i18n';
 beforeAll(async () => {
   await init({ fallbackLocale: 'dev' });
 });
+
+Object.defineProperty(globalThis, 'matchMedia', {
+  writable: true,
+  value: vi.fn().mockImplementation((query) => ({
+    matches: false,
+    media: query,
+    onchange: null,
+    addEventListener: vi.fn(),
+    removeEventListener: vi.fn(),
+    dispatchEvent: vi.fn(),
+  })),
+});