Migrate to eslint flat config file (#7)

.editorconfig

@@ -0,0 +1,6 @@
+[*.{js,jsx,mjs,cjs,ts,tsx,mts,cts,vue}]
+charset = utf-8
+indent_size = 2
+indent_style = space
+insert_final_newline = true
+trim_trailing_whitespace = true

eslint.config.js

@@ -0,0 +1,30 @@
+import pluginVue from 'eslint-plugin-vue'
+import vueTsEslintConfig from '@vue/eslint-config-typescript'
+import pluginVitest from '@vitest/eslint-plugin'
+
+export default [
+  {
+    name: 'app/files-to-lint',
+    files: ['**/*.{ts,mts,tsx,vue}'],
+  },
+
+  {
+    name: 'app/files-to-ignore',
+    ignores: ['**/dist/**', '**/dist-ssr/**', '**/coverage/**'],
+  },
+
+  ...pluginVue.configs['flat/essential'],
+  ...vueTsEslintConfig(),
+
+  {
+    ...pluginVitest.configs.recommended,
+    files: [
+      'tests/**/*.{j,t}s?(x)',
+      'src/**/__tests__/*'
+    ],
+    rules: {
+      '@typescript-eslint/no-unused-expressions': 'off'
+    },
+  },
+
+]