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-controlled.tsx

@@ -0,0 +1,14 @@
+import { Calendar } from "@medusajs/ui"
+import { useState } from "react"
+
+export default function CalendarControlled() {
+  const [date, setDate] = useState<Date | null>(null)
+  return (
+    <div className="flex flex-col gap-2">
+      <Calendar value={date} onChange={setDate} />
+      <span className="txt-small text-ui-fg-muted">
+        Selected: {date?.toDateString() ?? "None"}
+      </span>
+    </div>
+  )
+}