Restore ESLint and Prettier auto-formatting and CI linting (#1457)

* Restore ESLint and Prettier autoformatting

* Fix formatting and lints in web files

* Hacky fix to eslint crash

* Fix remaining lints

* Add lint-fix script

---------

Co-authored-by: 0hypercube <0hypercube@gmail.com>

frontend/.eslintrc.cjs

@@ -0,0 +1,96 @@
+module.exports = {
+	root: true,
+	env: { browser: true, node: true },
+	extends: [
+		"eslint:recommended",
+		"plugin:import/recommended",
+		"plugin:@typescript-eslint/recommended",
+		"plugin:import/typescript",
+		"plugin:svelte/recommended",
+		"plugin:svelte/prettier",
+		"prettier",
+	],
+	plugins: ["import", "@typescript-eslint", "prettier"],
+	settings: {
+		"import/parsers": { "@typescript-eslint/parser": [".ts", ".tsx"] },
+		"import/resolver": { typescript: true, node: true },
+	},
+	parser: "@typescript-eslint/parser",
+	parserOptions: {
+		ecmaVersion: "latest",
+		project: "./tsconfig.json",
+		extraFileExtensions: [".svelte"],
+	},
+	ignorePatterns: [
+		// Ignore generated directories
+		"node_modules/",
+		"dist/",
+		"pkg/",
+		"wasm/pkg/",
+		// Don't ignore JS and TS dotfiles in this folder
+		"!.*.js",
+		"!.*.ts",
+	],
+	overrides: [
+		{
+			files: ["*.js"],
+			rules: { "@typescript-eslint/explicit-function-return-type": ["off"] },
+		},
+		{
+			files: ["*.svelte"],
+			parser: "svelte-eslint-parser",
+			// Parse the `<script>` in `.svelte` as TypeScript by adding the following configuration.
+			parserOptions: { parser: "@typescript-eslint/parser" },
+		},
+	],
+	rules: {
+		// Standard ESLint config (for ordinary JS syntax linting)
+		indent: "off",
+		quotes: ["error", "double", { allowTemplateLiterals: true }],
+		camelcase: ["error", { properties: "always" }],
+		"linebreak-style": ["error", "unix"],
+		"eol-last": ["error", "always"],
+		"max-len": ["error", { code: 200, tabWidth: 4 }],
+		"prefer-destructuring": "off",
+		"no-console": "warn",
+		"no-debugger": "warn",
+		"no-param-reassign": ["error", { props: false }],
+		"no-bitwise": "off",
+		"no-shadow": "off",
+		"no-use-before-define": "off",
+		"no-restricted-imports": ["error", { patterns: [".*", "!@graphite/*"] }],
+
+		// TypeScript plugin config (for TS-specific linting)
+		"@typescript-eslint/indent": "off",
+		"@typescript-eslint/camelcase": "off",
+		"@typescript-eslint/no-use-before-define": "off",
+		"@typescript-eslint/no-unused-vars": ["error", { argsIgnorePattern: "^_", ignoreRestSiblings: true }],
+		"@typescript-eslint/consistent-type-imports": "error",
+		"@typescript-eslint/consistent-type-definitions": ["error", "type"],
+		"@typescript-eslint/consistent-type-assertions": ["error", { assertionStyle: "as", objectLiteralTypeAssertions: "never" }],
+		"@typescript-eslint/consistent-indexed-object-style": ["error", "record"],
+		"@typescript-eslint/consistent-generic-constructors": ["error", "constructor"],
+		"@typescript-eslint/ban-types": ["error", { types: { null: "Use `undefined` instead." } }],
+
+		// Prettier plugin config (for validating and fixing formatting)
+		"prettier/prettier": "error",
+
+		// Svelte plugin config (for validating Svelte-specific syntax)
+		"svelte/no-at-html-tags": "off",
+		"svelte/valid-compile": ["error", { ignoreWarnings: true }],
+
+		// Import plugin config (for intelligently validating module import statements)
+		"import/no-unresolved": "error",
+		"import/prefer-default-export": "off",
+		"import/no-relative-packages": "error",
+		"import/order": [
+			"error",
+			{
+				alphabetize: { order: "asc", caseInsensitive: true },
+				pathGroups: [{ pattern: "**/*.svelte", group: "unknown", position: "after" }],
+				"newlines-between": "always-and-inside-groups",
+				warnOnUnassignedImports: true,
+			},
+		],
+	},
+};