feat: Enhance Electron test harness with preload script and CSP configuration

test/electron/main.js

@@ -3,8 +3,7 @@ const path = require('path');
 
 /**
  * Creates the main application window.
- * nodeIntegration is enabled so the renderer can use require() / dynamic import()
- * directly against the local node_modules — appropriate for a local test harness.
+ * Uses a preload bridge so the renderer can stay in the safer default context.
  */
 function createWindow() {
   const win = new BrowserWindow({
@@ -12,8 +11,10 @@ function createWindow() {
     height: 800,
     backgroundColor: '#1a1a2e',
     webPreferences: {
-      nodeIntegration: true,
-      contextIsolation: false,
+      preload: path.join(__dirname, 'preload.js'),
+      sandbox: false,
+      nodeIntegration: false,
+      contextIsolation: true,
     },
   });