Bug report: Incorrect check for browser support in incognito mode

**Describe the bug**
I get the error message that my browser is not support in **incognito mode** even though it is supported.

**To Reproduce**
Steps to reproduce the behaviour or a link to the recipe / input used to cause the bug:

1. Go to cyberchef page.

**Expected behaviour**
Access to functions instead of locked screen.

**Screenshots**
```
CyberChef encountered an error while loading.

The following browser versions are supported:
Google Chrome 50+
Mozilla Firefox 38+
Your user agent is:
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/139.0.0.0 Safari/537.36

If your browser is supported, please [raise an issue](https://github.com/gchq/CyberChef/issues/new/choose) including the following details:
```

**Desktop (if relevant, please complete the following information):**
- OS: Windows
- Browser: chrome Version 139.0.7258.155 (Official Build) (64-bit)
- CyberChef version: [e.g. 9.7.14]

**Additional context**
Uncaught TypeError: Cannot read properties of null (reading 'addEventListener')
Filename: https://cyberchef.viskanint.local/assets/main.js
Line: 2
Column: 8211627
Error: TypeError: Cannot read properties of null (reading 'addEventListener')
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/139.0.0.0 Safari/537.36
CyberChef version: 10.8.2

The report identifies the deployed assets/main.js error and the CyberChef page as the reproduction entry point, but no source file or test is named. Start by reproducing the loading failure in Chrome incognito and trace the browser-support or startup path to the null addEventListener call. Done means supported Chrome loads CyberChef and reaches its functions instead of the locked screen.

Written by the indexing model from the issue text.