build: implement bundling system with Rollup

Phase 1-3 Complete:
- ✅ Installed Rollup with all required plugins
- ✅ Created rollup.config.js for UMD, ESM, CJS builds
- ✅ Created src/index.js entry point
- ✅ Created src/styles.css for CSS bundling
- ✅ Added ES6 exports to debug-system.js
- ✅ Excluded Node.js-only html-generator.js from bundle

Build outputs:
- dist/testdrive-jsui.js (217KB UMD)
- dist/testdrive-jsui.min.js (107KB minified!)
- dist/testdrive-jsui.esm.js (199KB ES Module)
- dist/testdrive-jsui.cjs.js (199KB CommonJS)
- dist/testdrive-jsui.css (minified, all styles inlined)

All builds include source maps for debugging.

src/index.js

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+/**
+ * TestDrive-JSUI - Main Entry Point
+ *
+ * This file bundles all components into a single distributable library.
+ *
+ * @version 1.0.0
+ * @license MIT
+ */
+
+// Import CSS (will be extracted by postcss plugin)
+import './styles.css';
+
+// Core components (must be loaded first)
+import '../js/core/debug-system.js';
+import '../js/core/section-manager.js';
+
+// UI Components
+import '../js/components/dom-renderer.js';
+import '../js/components/document-controls.js';
+import '../js/components/debug-panel.js';
+
+// Control panels
+import '../js/controls/control-base.js';
+import '../js/controls/edit-control.js';
+import '../js/controls/debug-control.js';
+import '../js/controls/status-control.js';
+import '../js/controls/contents-control.js';
+
+// Utilities
+import '../js/config-loader.js';
+// Note: html-generator.js is Node.js only (uses 'fs'), excluded from browser bundle
+
+// Widgets (if needed)
+import '../js/widgets/base/Widget.js';
+import '../js/widgets/base/UIWidget.js';
+import '../js/widgets/navigation/DocumentNavigator.js';
+
+// Plugins
+import '../js/plugins/document-navigator-plugin.js';
+
+// Main library class
+// Note: testdrive-jsui.js already exports in multiple formats
+// We'll import it and re-export
+
+// The main class is defined in testdrive-jsui.js
+// Since all dependencies are loaded above, we can now load the main class
+import '../js/testdrive-jsui.js';
+
+// Get the TestDriveJSUI from window (set by testdrive-jsui.js)
+// In UMD build, this will be available globally
+const TestDriveJSUI = (typeof window !== 'undefined' && window.TestDriveJSUI)
+  || (typeof global !== 'undefined' && global.TestDriveJSUI);
+
+// Export for ES modules and CommonJS
+export default TestDriveJSUI;
+export { TestDriveJSUI };
+
+// Export version
+export const version = '1.0.0';

src/styles.css

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+/**
+ * TestDrive-JSUI Styles
+ * Combined stylesheet for the markdown editor
+ *
+ * @version 1.0.0
+ * @license MIT
+ */
+
+/* Base editor styles */
+@import '../static/css/editor.css';
+
+/* Control panels */
+@import '../static/css/controls.css';
+
+/* Default theme (GitHub) */
+@import '../static/css/themes/github.css';
+
+/* CSS Variables and Base Styles */
+:root {
+  --testdrive-primary-color: #0366d6;
+  --testdrive-border-color: #e1e4e8;
+  --testdrive-background: #ffffff;
+  --testdrive-text-color: #24292e;
+  --testdrive-hover-bg: #f6f8fa;
+  --testdrive-focus-shadow: rgba(3, 102, 214, 0.3);
+}
+
+.testdrive-container {
+  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Helvetica, Arial, sans-serif;
+  line-height: 1.6;
+  color: var(--testdrive-text-color);
+  background: var(--testdrive-background);
+}
+
+/* Ensure smooth transitions */
+* {
+  transition: background-color 0.2s ease, border-color 0.2s ease;
+}