Initial commit: Developer Tools MVP with visual editor

- Complete React app with 7 developer tools
- JSON Tool with visual structured editor
- Serialize Tool with visual structured editor
- URL, Base64, CSV/JSON, Beautifier, Diff tools
- Responsive navigation with dropdown menu
- Dark/light mode toggle
- Mobile-responsive design with sticky header
- All tools working with copy/paste functionality

node_modules/eslint/lib/rules/utils/regular-expressions.js

@@ -0,0 +1,42 @@
+/**
+ * @fileoverview Common utils for regular expressions.
+ * @author Josh Goldberg
+ * @author Toru Nagashima
+ */
+
+"use strict";
+
+const { RegExpValidator } = require("@eslint-community/regexpp");
+
+const REGEXPP_LATEST_ECMA_VERSION = 2024;
+
+/**
+ * Checks if the given regular expression pattern would be valid with the `u` flag.
+ * @param {number} ecmaVersion ECMAScript version to parse in.
+ * @param {string} pattern The regular expression pattern to verify.
+ * @returns {boolean} `true` if the pattern would be valid with the `u` flag.
+ * `false` if the pattern would be invalid with the `u` flag or the configured
+ * ecmaVersion doesn't support the `u` flag.
+ */
+function isValidWithUnicodeFlag(ecmaVersion, pattern) {
+    if (ecmaVersion <= 5) { // ecmaVersion <= 5 doesn't support the 'u' flag
+        return false;
+    }
+
+    const validator = new RegExpValidator({
+        ecmaVersion: Math.min(ecmaVersion, REGEXPP_LATEST_ECMA_VERSION)
+    });
+
+    try {
+        validator.validatePattern(pattern, void 0, void 0, { unicode: /* uFlag = */ true });
+    } catch {
+        return false;
+    }
+
+    return true;
+}
+
+module.exports = {
+    isValidWithUnicodeFlag,
+    REGEXPP_LATEST_ECMA_VERSION
+};