Resolve linter issues, add unit tests, adjust test coverage

qr-web/eslint.config.cjs

@@ -0,0 +1,18 @@
+'use strict';
+
+const nextConfig = require('eslint-config-next/core-web-vitals');
+const prettierConfig = require('eslint-config-prettier');
+
+module.exports = [
+    ...nextConfig,
+    prettierConfig,
+    {
+        files: ['**/*.ts', '**/*.tsx'],
+        rules: {
+            '@typescript-eslint/no-unused-vars': [
+                'warn',
+                { argsIgnorePattern: '^_' },
+            ],
+        },
+    },
+];