docs: migrate UI docs (#13245)

* docs: create a new UI docs project (#13233)

* docs: create a new UI docs project

* fix installation errors

* docs: migrate UI docs content to new project (#13241)

* Fix content

* added examples for some components

* finish adding examples

* lint fix

* fix build errors

* delete empty files

* path fixes + refactor

* fix build error

www/apps/ui/specs/examples/calendar-demo.tsx

@@ -0,0 +1,8 @@
+import { Calendar } from "@medusajs/ui"
+import * as React from "react"
+
+export default function CalendarDemo() {
+  const [date, setDate] = React.useState<Date | null>()
+
+  return <Calendar value={date} onChange={setDate} />
+}