Set up comprehensive frontend testing infrastructure

- Install Jest for unit testing with React Testing Library
- Install Playwright for end-to-end testing
- Configure Jest with proper TypeScript support and module mapping
- Create test setup files and utilities for both unit and e2e tests

Components:
* Jest configuration with coverage thresholds
* Playwright configuration with browser automation
* Unit tests for LoginForm, AuthContext, and useSocketIO hook
* E2E tests for authentication, dashboard, and agents workflows
* GitHub Actions workflow for automated testing
* Mock data and API utilities for consistent testing
* Test documentation with best practices

Testing features:
- Unit tests with 70% coverage threshold
- E2E tests with API mocking and user journey testing
- CI/CD integration for automated test runs
- Cross-browser testing support with Playwright
- Authentication system testing end-to-end

🚀 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

frontend/node_modules/symbol-tree/lib/SymbolTreeNode.js

@@ -0,0 +1,54 @@
+'use strict';
+
+module.exports = class SymbolTreeNode {
+        constructor() {
+                this.parent = null;
+                this.previousSibling = null;
+                this.nextSibling = null;
+
+                this.firstChild = null;
+                this.lastChild = null;
+
+                /** This value is incremented anytime a children is added or removed */
+                this.childrenVersion = 0;
+                /** The last child object which has a cached index */
+                this.childIndexCachedUpTo = null;
+
+                /** This value represents the cached node index, as long as
+                 * cachedIndexVersion matches with the childrenVersion of the parent */
+                this.cachedIndex = -1;
+                this.cachedIndexVersion = NaN; // NaN is never equal to anything
+        }
+
+        get isAttached() {
+                return Boolean(this.parent || this.previousSibling || this.nextSibling);
+        }
+
+        get hasChildren() {
+                return Boolean(this.firstChild);
+        }
+
+        childrenChanged() {
+                /* jshint -W016 */
+                // integer wrap around
+                this.childrenVersion = (this.childrenVersion + 1) & 0xFFFFFFFF;
+                this.childIndexCachedUpTo = null;
+        }
+
+        getCachedIndex(parentNode) {
+                // (assumes parentNode is actually the parent)
+                if (this.cachedIndexVersion !== parentNode.childrenVersion) {
+                        this.cachedIndexVersion = NaN;
+                        // cachedIndex is no longer valid
+                        return -1;
+                }
+
+                return this.cachedIndex; // -1 if not cached
+        }
+
+        setCachedIndex(parentNode, index) {
+                // (assumes parentNode is actually the parent)
+                this.cachedIndexVersion = parentNode.childrenVersion;
+                this.cachedIndex = index;
+        }
+};