Merge main into gallery-embed, migrate off local shim

Bumps @atproto/api to 0.20.9, which ships the generated
`AppBskyEmbedGallery` namespace and `DraftPost.embedGallery`. Swaps every
`#/lib/api/gallery-embed-shim` import to `@atproto/api`, deletes the
shim, drops the local `DraftPostWithGallery` widen-types, and adds the
narrowing calls (`isViewImage`, `isDraftEmbedImage`) the real lexicon
unions require.

The merge also auto-resolves an inline image-restore block in
`drafts/state/api.ts` against main's typing tweak — main switched to
`satisfies ComposerImage` and `NonNullable<typeof img>`, which here move
into the existing `restoreDraftImages` helper that's now shared by both
the images and gallery restore paths.

src/types/bsky/post.ts

@@ -1,6 +1,7 @@
 import {
   type $Typed,
   AppBskyEmbedExternal,
+  AppBskyEmbedGallery,
   AppBskyEmbedImages,
   AppBskyEmbedRecord,
   AppBskyEmbedRecordWithMedia,
@@ -10,8 +11,6 @@ import {
   AppBskyLabelerDefs,
 } from '@atproto/api'
 
-import {AppBskyEmbedGallery} from '#/lib/api/gallery-embed-shim'
-
 export type Embed =
   | {
       type: 'post'