style: fix lint errors in test files

- Remove unused imports in config.test.ts and conversations.test.ts
- Remove unused handler variable in tauri.test.ts
- Remove unused _args parameter in vitest.setup.ts mock
- Add coverage/ to eslint ignore list

src/lib/stores/config.test.ts

@@ -1,11 +1,6 @@
 import { describe, it, expect, beforeEach, vi } from "vitest";
-import { get } from "svelte/store";
 import {
   configStore,
-  isDarkTheme,
-  isStreamerMode,
-  isCompactMode,
-  shouldHidePaths,
   maskPaths,
   clampFontSize,
   applyFontSize,