Set up downloadable builds through Tauri

[Keavon]

Tauri is an Electron alternative that uses the local OS's webview to provide a low-overhead web wrapper as a desktop app. It's part of the Rust ecosystem. This is actually something we can tackle sooner than I was previously expecting.

• [ ] We should probably wait to switch to Svelte (#635), but this isn't a strict blocker
• [x] We should probably wait for Tauri's official 1.0 release ~~(as of writing, it's at the release candidate stage)~~ (Released)
• [ ] We will want to configure our build infrastructure to provide binaries and automatic updates as part of the deployment process
• [ ] And we'll want to add some in-app functionality to nicely prompt to install updates

Longer-term:

• We'll want to run the Rust code natively instead of inside the webview's WASM runtime, especially once we're doing our own rendering rather than using the browser's SVG engine (since the perf bottleneck is currently on that render engine, not ours)
• Tauri will be useful for hosting the Monaco code editor for node source code editing