fix(frontend): GIFバナーの復活など (#10247)

* Restore GIF banner

* Add ALT banner, detect APNG too

* Add vitest

* Add CI for vitest

* Upload coverage?

* frontend

packages/frontend/test/init.ts

@@ -0,0 +1,18 @@
+import { vi } from 'vitest';
+
+// Set i18n
+import locales from '../../../locales';
+import { updateI18n } from '@/i18n';
+updateI18n(locales['en-US']);
+
+// XXX: misskey-js panics if WebSocket is not defined
+vi.stubGlobal('WebSocket', class WebSocket extends EventTarget { static CLOSING = 2; });
+
+// XXX: defaultStore somehow becomes undefined in vitest?
+vi.mock('@/store.js', () => {
+	return {
+		defaultStore: {
+			state: {},
+		},
+	};
+});