fix: sync eslint config with upstream

-
https://eslint.org/docs/latest/use/migrate-to-9.0.0#-new-default-config-format-eslintconfigjs
-
https://github.com/sveltejs/kit/blob/feb01542edd542366043bc4f3b1994e3fdb46345/packages/create-svelte/shared/%2Beslint%2Bprettier%2Btypescript/eslint.config.js

Author: 0x2E

frontend/.eslintignore

@@ -1,31 +1,33 @@
-/** @type { import("eslint").Linter.Config } */
-module.exports = {
-	root: true,
-	extends: [
-		'eslint:recommended',
-		'plugin:@typescript-eslint/recommended',
-		'plugin:svelte/recommended',
-		'prettier'
-	],
-	parser: '@typescript-eslint/parser',
-	plugins: ['@typescript-eslint'],
-	parserOptions: {
-		sourceType: 'module',
-		ecmaVersion: 2020,
-		extraFileExtensions: ['.svelte']
-	},
-	env: {
-		browser: true,
-		es2017: true,
-		node: true
+import js from '@eslint/js';
+import ts from 'typescript-eslint';
+import svelte from 'eslint-plugin-svelte';
+import prettier from 'eslint-config-prettier';
+import globals from 'globals';
+
+/** @type {import('eslint').Linter.Config[]} */
+export default [
+	js.configs.recommended,
+	...ts.configs.recommended,
+	...svelte.configs['flat/recommended'],
+	prettier,
+	...svelte.configs['flat/prettier'],
+	{
+		languageOptions: {
+			globals: {
+				...globals.browser,
+				...globals.node
+			}
+		}
 	},
-	overrides: [
-		{
-			files: ['*.svelte'],
-			parser: 'svelte-eslint-parser',
+	{
+		files: ['**/*.svelte'],
+		languageOptions: {
 			parserOptions: {
-				parser: '@typescript-eslint/parser'
+				parser: ts.parser
 			}
 		}
-	]
-};
+	},
+	{
+		ignores: ['build/', '.svelte-kit/', 'dist/']
+	}
+];

frontend/.eslintrc.cjs

@@ -0,0 +1,33 @@
+import js from '@eslint/js';
+import ts from 'typescript-eslint';
+import svelte from 'eslint-plugin-svelte';
+import prettier from 'eslint-config-prettier';
+import globals from 'globals';
+
+/** @type {import('eslint').Linter.Config[]} */
+export default [
+	js.configs.recommended,
+	...ts.configs.recommended,
+	...svelte.configs['flat/recommended'],
+	prettier,
+	...svelte.configs['flat/prettier'],
+	{
+		languageOptions: {
+			globals: {
+				...globals.browser,
+				...globals.node
+			}
+		}
+	},
+	{
+		files: ['**/*.svelte'],
+		languageOptions: {
+			parserOptions: {
+				parser: ts.parser
+			}
+		}
+	},
+	{
+		ignores: ['build/', '.svelte-kit/', 'dist/']
+	}
+];