Single-object viewer POC (#14)

This commit implements a Sketchfab-style single-object viewer as a minimal
proof-of-concept.

### `@storyteller/studio-web`
This is a new package to house web components for interfacing with the
`@storyteller/studio` WASM library. It currently includes a single component,
`<sts-viewer />`, which is exported from `@storyteller/studio-web/viewer`.

### `react-frontend`
This is a new application intended as a proof-of-concept and testbed for React
interop with `@storyteller/studio-web`.

Web components are currently a little bit fiddly to use in a React application.
`react-frontend/src/app/studio-viewer.tsx` demonstrates how a React-idiomatic
component can be written as a thin wrapper around a web component, and
`react-frontend/src/app/app.tsx` demonstrates that wrapper component in use.

studio/src/inspector/mod.rs

@@ -0,0 +1,16 @@
+use bevy::prelude::*;
+
+#[cfg(feature = "wasm")]
+mod wasm;
+
+pub struct InspectorPlugin;
+
+impl Plugin for InspectorPlugin {
+    fn build(&self, app: &mut App) {
+        #[cfg(feature = "wasm")]
+        app.add_systems(
+            PostUpdate,
+            wasm::notify_entity_spawn_changes.map(bevy::utils::error),
+        );
+    }
+}