**Add Vitest support and migrate frontend tests**

- Added Vitest configuration (`vitest.config.mjs`) for frontend unit testing with a `jsdom` environment.
- Migrated and rewrote key frontend tests (`api.test.js`, `comiclist.test.js`, `comicreader.test.js`, `historytable.test.js`, `router.test.js`, `store.test.js`) to Vitest, improving maintainability.
- Removed `tsconfig.json` and related TypeScript loaders from `webpack` configurations (`webpack.dev.js`, `webpack.prod.js`).
- Adjusted `eslint.config.mjs` to support Vitest tests.
- Updated `package-lock.json` to include Vitest, test utilities (`jsdom`, `@vue/test-utils`), and other associated packages.
- Updated Nginx configuration for better compression on assets (`gzip` adjustments).
- Enhanced `entrypoint.sh` to include first-run library indexing (`--if-empty` argument).
- Simplified the `scan_comics` command with a dedicated test for empty database scans.

This transition improves testing workflows and backend/frontend synergy while removing unused TypeScript dependencies.

frontend/eslint.config.mjs

@@ -22,6 +22,23 @@ export default [
     },
   },
 
+  // Tests run under Vitest with a jsdom environment.
+  {
+    files: ['test/**'],
+    languageOptions: {
+      ecmaVersion: 2022,
+      sourceType: 'module',
+      globals: {
+        document: 'readonly',
+        localStorage: 'readonly',
+        console: 'readonly',
+        window: 'readonly',
+        HTMLElement: 'readonly',
+        KeyboardEvent: 'readonly',
+      },
+    },
+  },
+
   // Application code is browser code bundled by webpack.
   {
     files: ['src/**'],