Add foliate-js submodule with import alias

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "web/vendor/foliate-js"]
+	path = web/vendor/foliate-js
+	url = git@github.com:john-okeefe/foliate-js.git

vite.config.ts

@@ -1,5 +1,11 @@
 import { defineConfig } from "vite";
 export default defineConfig({
+  resolve: {
+    alias: {
+      "@": "/web/src",
+      "foliate-js": "/web/vendor/foliate-js",
+    },
+  },
   base: "/static/",
   build: {
     outDir: "web/static",