finish phase 3: type-only codemod and zero non-bridge @atproto/api imports

Task 8: codemod repointed 150 namespace-type files to #/lexicons
(AppBskyFeedDefs.PostView -> app.bsky.feed.defs.PostView, .Record -> .Main)
plus ~105 hand-fixed consumers (composer/video state, DebugMod, Profile,
onboarding, dialogs). DM_SERVICE_HEADERS deleted; last chat call sites on
the chat client. RichText.tsx flipped to SDK-only. Remaining @atproto/api
importers: the three session bridge files, the deliberate dual-world
matcher in lib/xrpc-error.ts, and test fixtures. toLex boundary casts are
TODO(phase4)-tagged for bridge removal.

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

src/state/unstable-post-source.tsx

@@ -1,8 +1,9 @@
 import {useEffect, useId, useState} from 'react'
-import {type AppBskyFeedDefs, AtUri} from '@atproto/api'
+import {AtUri} from '@atproto/syntax'
 
 import {Logger} from '#/logger'
 import {type FeedSourceInfo} from '#/state/queries/feed'
+import {type app} from '#/lexicons'
 
 /**
  * Separate logger for better debugging
@@ -10,7 +11,7 @@ import {type FeedSourceInfo} from '#/state/queries/feed'
 const logger = Logger.create(Logger.Context.PostSource)
 
 export type PostSource = {
-  post: AppBskyFeedDefs.FeedViewPost
+  post: app.bsky.feed.defs.FeedViewPost
   feedSourceInfo?: FeedSourceInfo
 }