fix: add setWindowOpenHandler for external links

Restores the handler that opens target="_blank" links in the default
browser instead of trying to create a new Electron window.

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/app/electron/main.js

@@ -131,6 +131,12 @@ function createWindow() {
   mainWindow.on("closed", () => {
     mainWindow = null;
   });
+
+  // Handle external links - open in default browser
+  mainWindow.webContents.setWindowOpenHandler(({ url }) => {
+    shell.openExternal(url);
+    return { action: "deny" };
+  });
 }
 
 // App lifecycle