lazy load @ipld/dag-cbor in computeCid

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/lib/api/index.ts

@@ -16,7 +16,6 @@ import {
   RichText,
 } from '@atproto/api'
 import {TID} from '@atproto/common-web'
-import * as dcbor from '@ipld/dag-cbor'
 import {t} from '@lingui/core/macro'
 import {type QueryClient} from '@tanstack/react-query'
 import {sha256} from 'js-sha256'
@@ -505,6 +504,12 @@ const mf_sha256 = Hasher.from({
 })
 
 async function computeCid(record: AppBskyFeedPost.Record): Promise<string> {
+  /*
+   * Lazily loaded since it's only needed when posting a thread, and its
+   * `cborg` dependency is ~190KB that would otherwise be in the initial
+   * web bundle.
+   */
+  const dcbor = await import('@ipld/dag-cbor')
   // IMPORTANT: `prepareObject` prepares the record to be hashed by removing
   // fields with undefined value, and converting BlobRef instances to the
   // right IPLD representation.