Clarify and unify AdGuard Assistant and browser extension integration in Windows desktop app

### Issue Details

### Description

I want to use the AdGuard browser-management feature, but I am currently confused because there appear to be two separate features with very similar or overlapping names within the AdGuard for Windows app.

#### Steps to Reproduce / Where I Found This

1. Open AdGuard for Windows and navigate to the **Protection** tab.
2. Under the main options, the first setting says **"Control AdGuard from your browser"**. Clicking this prompts the installation of a browser extension.
3. Further down on the same **Protection** page, there is a setting called **"Extensions"**.
4. Clicking into **Extensions** shows the first item listed as **"AdGuard Assistant"** (a userscript).

#### Documentation / Help Page Comparison

I checked the documentation for both features to see how they differ:

* **Browser Extension Help Page:** [[adguard.com/en/adguard-assistant/overview.html](https://adguard.com/en/adguard-assistant/overview.html#firefox)]
> *"A companion browser extension for AdGuard desktop apps. It allows you to block custom items on websites, add websites to allowlist, and send reports directly from your browser."*

* **Userscript / GitHub Page:** [[github.com/AdguardTeam/AdguardAssistant](https://github.com/AdguardTeam/AdguardAssistant)]
> *"AdGuard Assistant is a userscript that helps you manage filtering right from the browser. With its aid you are able to manually block any element, whitelist or report the page, or see the website's security report — all without having to leave the current page."*

Both descriptions outline almost identical core capabilities (element blocking, allowlisting, reporting), which makes it unclear why both options exist side-by-side.

#### Questions

1. Which of these two options is recommended for regular usage, and what is the intended distinction between them?
2. Is it sufficient to install only the browser extension and leave the userscript unchecked/disabled? Are any features missed by doing this?
3. Conversely, what happens if I only use the built-in userscript and not the browser extension?
4. What happens if both options are enabled simultaneously? Does it cause conflicts?

### Proposed solution

It would be much more user-friendly to streamline this down into a single, unified option rather than offering two separate paths. Since users have already installed a system-wide desktop application, it can feel redundant to require an additional web browser extension just to manage basic on-page controls. Ideally, core management features like element blocking and allowlisting should be handled seamlessly through the desktop app or a single integrated mechanism without requiring extra manual extension installations.

### Alternative solution

N/A