Prepare for an eventual frontend

Move the backend code into a backend/ directory, and create a frontend/
directory containing an empty sveltekit project.

backend/src/main.rs

@@ -0,0 +1,50 @@
+use async_graphql::http::GraphiQLSource;
+use async_graphql_axum::{GraphQLRequest, GraphQLResponse};
+use axum::{
+    Router,
+    response::Html,
+    routing::{get, post},
+};
+use std::net::SocketAddr;
+
+mod models;
+mod resolvers;
+mod schema;
+
+#[tokio::main]
+async fn main() -> anyhow::Result<()> {
+    let schema = schema::build_schema().await?;
+
+    let app = Router::new()
+        .route(
+            "/graphql",
+            post({
+                let schema = schema.clone();
+                move |req: GraphQLRequest| async move {
+                    GraphQLResponse::from(schema.execute(req.into_inner()).await)
+                }
+            }),
+        )
+        .route(
+            "/graphql",
+            get({
+                let schema = schema.clone();
+                move || async move { axum::Json(schema.sdl()) }
+            }),
+        )
+        .route(
+            "/graphiql",
+            get(Html(GraphiQLSource::build().endpoint("/graphql").finish())),
+        );
+
+    let addr = SocketAddr::from(([127, 0, 0, 1], 3000));
+    println!("listening on http://{}", addr);
+
+    axum::serve(
+        tokio::net::TcpListener::bind(addr).await.unwrap(),
+        app.into_make_service(),
+    )
+    .await
+    .unwrap();
+    Ok(())
+}