[Embeds] Embed subdomain landing page (#3501)

* add build output to web build

* simplify post-build step by copying everything at once

* make script that converts placeholder -> iframe

* dynamically resize iframe based on inner content

Requires the iframe content to `postMessage` its height back up to the parent

* add lang to embed

* svg explicit height -> viewBox

* add build output to web build

* simplify post-build step by copying everything at once

* attempt to fix go embed issue

* rm changes to bskyweb

* remove another bskyweb change

* embed landing page

* Drop xl breakpoint, too far down

* Remove pointer enter behavior

* Avoid button width jump

* Escape HTML

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Co-authored-by: Dan Abramov <dan.abramov@gmail.com>

bskyembed/src/components/link.tsx

@@ -0,0 +1,21 @@
+import {h} from 'preact'
+
+export function Link({
+  href,
+  className,
+  ...props
+}: {
+  href: string
+  className?: string
+} & h.JSX.HTMLAttributes<HTMLAnchorElement>) {
+  return (
+    <a
+      href={href.startsWith('http') ? href : `https://bsky.app${href}`}
+      target="_blank"
+      rel="noopener noreferrer nofollow"
+      onClick={evt => evt.stopPropagation()}
+      className={`cursor-pointer ${className || ''}`}
+      {...props}
+    />
+  )
+}