Replace bootstrap methods with async factories

Controller.bootstrap and Host.bootstrap returned constructor arguments
that the caller had to spread into new Controller/Host, and
DatastoreProvider.bootstrap did the same for datastores. They are
replaced by Controller.fromConfig, Host.fromConfig and
KeyValueDatastore/SubscribableDatastore.fromProvider, which load the
data and return the finished instance.

Closes #1126

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/host/host.ts

@@ -233,13 +233,12 @@ async function startHost() {
 	}
 
 	let hostConnector = new HostConnector(hostConfig, pluginInfos);
-	host = new Host(
+	host = await Host.fromConfig(
 		hostConnector,
 		hostConfig,
 		pluginInfos,
 		Boolean(args.canRestart),
 		Boolean(args.recovery),
-		...await Host.bootstrap(hostConfig)
 	);
 
 	// Handle interrupts