kit: Bundle kit in build step

Author: GrygrFlzr

Diff for: .changeset/weak-swans-lie.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+kit: bundle @sveltejs/kit into built application

Diff for: packages/kit/src/core/build/index.js

@@ -389,7 +389,7 @@ async function build_server(
 			})
 		],
 		ssr: {
-			noExternal: ['svelte']
+			noExternal: ['svelte', '@sveltejs/kit']
 		},
 		optimizeDeps: {
 			entries: []