collapse the dual-world type layer and delete the widening shims

The types/bsky post/profile/starterPack unions drop their @atproto/api arms,
and dangerousIsType/validate go with the old-world guards they wrapped. The
moderation subjects.ts widening shim and rich-text-helpers' asSdkFacets both
existed only to bridge branded and unbranded views, so their 55 and 14 callers
now go straight to @bsky.app/sdk/moderation and the raw facets.

Boundary fallout: lexicon token defs are camelCase schema objects needing
.value, and the branded string slots that the widening used to absorb are now
cast or branded at their producers.

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

src/components/Post/Embed/FeedEmbed.tsx

@@ -1,6 +1,6 @@
 import {useMemo} from 'react'
 
-import {moderateFeedGenerator} from '#/lib/moderation/subjects'
+import {moderateFeedGenerator} from '@bsky.app/sdk/moderation'
 import {useModerationOpts} from '#/state/preferences/moderation-opts'
 import {atoms as a, useTheme} from '#/alf'
 import * as FeedCard from '#/components/FeedCard'