tauri-plugin-opener: mobile support

I'm sorry if this is a duplicate. I can see that support for iOS and Android in tauri-plugin-opener are marked with `?`, but I could not find an open issue.

For my oauth flow I need to open a browser window, but this seems to break on iOS. It works on desktop.

* iOS version: 26.0 (23A5326a)
* Tauri version: 2.8.4
* tauri-plugin-opener version: 2.2.3
* Capability permissions: ["core:default", "opener:default", "shell:default", "store:default"]

Simplified code:
```
tauri_plugin_opener::open_url("https://www.google.com", None::<&str>)
.map_err(|err| err.to_string())?;
```

Error received: `Operation not permitted (os error 1)`