[Feature] Support for Safari: good news is it basically working.

I just tried to convert the Firefox version (dist/firefox) to Safari extension.

Good news is it basically working.

1. it can connect to the AB Downloader application
2. it can open the settings page (but changing settings seems not working)
3. it can start a download task from right click
4. it can fetch download links (but Safari will also start one at same time)

Bad news is there are warnings from XCode and Manifest V3 (Chrome version) not working.

```
Xcode Project Location: ...
App Name: AB Download Manager Browser Integration
App Bundle Identifier: ...
Platform: macOS
Language: Swift
Warning: The following keys in your manifest.json are not supported by your current version of Safari. If these are critical to your extension, you should review your code to see if you need to make changes to support Safari:
downloads
webRequestBlocking
open_in_tab
notifications
```

Error for V3 (tranlated by GPT):

```
非持續背景內容無法聆聽 webRequest 事件。
```

```
Non-persistent background content cannot listen to webRequest events.
```

But V3 is recommended for the future.