style: fix strict clippy and TypeScript type errors

- Fix assertions on constants in clipboard.rs (use const blocks)
- Fix unnecessary unwrap after is_ok check in git.rs
- Remove redundant u64 >= 0 comparison in stats.rs
- Add #[allow(clippy::useless_vec)] to sorting tests
- Add missing beforeEach import to vitest.setup.ts
- Change global.Audio to globalThis.Audio in notifications.test.ts
- Add type annotations to fix null type narrowing in conversations.test.ts

vitest.setup.ts

@@ -1,5 +1,5 @@
 import "@testing-library/jest-dom/vitest";
-import { vi } from "vitest";
+import { vi, beforeEach } from "vitest";
 
 // Mock Tauri invoke API
 const mockInvokeResults: Record<string, unknown> = {};