Resolve linter issues, add unit tests, adjust test coverage

qr-web/vitest.config.ts

@@ -8,6 +8,18 @@ export default defineConfig({
         environment: 'jsdom',
         globals: false,
         include: ['src/**/*.test.{ts,tsx}'],
+        coverage: {
+            provider: 'v8',
+            reporter: ['text', 'lcov'],
+            include: ['src/lib/**/*.ts', 'src/types/**/*.ts'],
+            exclude: ['src/**/*.test.{ts,tsx}'],
+            thresholds: {
+                lines: 80,
+                functions: 80,
+                branches: 80,
+                statements: 80,
+            },
+        },
     },
     resolve: {
         alias: { '@': path.resolve(__dirname, './src') },