[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/utils.ts

@@ -1,3 +1,5 @@
+import {AtUri} from '@atproto/api'
+
 export function niceDate(date: number | string | Date) {
   const d = new Date(date)
   return `${d.toLocaleDateString('en-us', {
@@ -11,5 +13,6 @@ export function niceDate(date: number | string | Date) {
 }
 
 export function getRkey({uri}: {uri: string}): string {
-  return uri.split('/').pop() as string
+  const at = new AtUri(uri)
+  return at.rkey
 }