Installing Dev Extensions with sandboxing disabled fails due to missing rustup

I was able to install a Dev Extension [such as the DotRush C# server in Zed by installing `rustup`](https://github.com/JaneySprings/DotRush/blob/main/src/Zed/Readme.md) on the host with some fiddling. However, with the sandbox disabled, I cannot get it to compile, not even when the Rust Flatpak SDK is installed and has its `bin` folder added to `PATH` using Flatseal.

This may be due to to `rustup` not being part of the Flatpak SDK, as the Zed logs say this:

```
2025-07-04T09:46:19+02:00 INFO [extension::extension_builder] compiling Rust extension /home/user/Downloads/JaneySprings DotRush main src-Zed
2025-07-04T09:46:19+02:00 WARN [home] failed to compile Rust extension

Caused by:
0: failed to run `rustup target add`
1: No such file or directory (os error 2)
2025-07-04T09:46:19+02:00 ERROR [extensions_ui] Failed to install dev extension: failed to compile Rust extension

Caused by:
0: failed to run `rustup target add`
1: No such file or directory (os error 2)
```

I'm not sure if the best path forward is to have rustup be added to the Flatpak Rust SDK or to have Zed use `rustc` or similar directly.