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/session/index.tsx

@@ -8,7 +8,6 @@ import {
   useState,
   useSyncExternalStore,
 } from 'react'
-import {type AtpSessionEvent} from '@atproto/api'
 import {type Client} from '@atproto/lex-client'
 import {PasswordSession} from '@atproto/lex-password-session'
 
@@ -22,6 +21,7 @@ import {emitSessionDropped} from '../events'
 import {getPublicLexClient, getUnauthenticatedClient} from './clients'
 import {type Action, getInitialState, reducer, type State} from './reducer'
 import {
+  type AtpSessionEvent,
   buildBundle,
   createSessionBundleAndCreateAccount,
   createSessionBundleAndLogin,