rework session layer on PasswordSession + three-client pattern

- PasswordSession (@atproto/lex-password-session) is now the single auth
  core; SessionAgent bridges it to the base Agent from @atproto/api so
  the ~148 useAgent() consumer files keep working unchanged
- SessionBundle carries {session, agent, accountClient, appviewClient};
  useLexClient() now returns the authed appview client, new
  useAppviewClient()/usePdsClient() hooks
- reducer: OpaqueSessionBundle, new replaced-current-bundle action for
  network-free cross-tab same-did sync (PasswordSession is immutable, so
  the bundle is rebuilt instead of mutated in place)
- moderation: AtpAgent.configure -> Client.configure + Agent.configure,
  per-account labelers on both the bridge and the appview client
- push-token unregistration uses temporary PasswordSessions
- hard-tail migrations: SignupQueued refresh via resumeSession shim,
  useBeginAgeAssurance scoped-token raw Client, useAccountEmailState
  reads currentAccount
- PDS routing preserved on the no-network resume fast path by
  synthesizing a minimal didDoc from the persisted pdsUrl

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

src/lib/api/feed/following.ts

@@ -1,11 +1,12 @@
-import {type AppBskyFeedDefs, type AtpAgent} from '@atproto/api'
+import {type AppBskyFeedDefs} from '@atproto/api'
 
+import {type SessionAgent} from '#/state/session'
 import {type FeedAPI, type FeedAPIResponse} from './types'
 
 export class FollowingFeedAPI implements FeedAPI {
-  agent: AtpAgent
+  agent: SessionAgent
 
-  constructor({agent}: {agent: AtpAgent}) {
+  constructor({agent}: {agent: SessionAgent}) {
     this.agent = agent
   }