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/merge.ts

@@ -1,8 +1,4 @@
-import {
-  type AppBskyFeedDefs,
-  type AppBskyFeedGetTimeline,
-  type AtpAgent,
-} from '@atproto/api'
+import {type AppBskyFeedDefs, type AppBskyFeedGetTimeline} from '@atproto/api'
 import shuffle from 'lodash.shuffle'
 
 import {bundleAsync} from '#/lib/async/bundle'
@@ -10,6 +6,7 @@ import {timeout} from '#/lib/async/timeout'
 import {feedUriToHref} from '#/lib/strings/url-helpers'
 import {getContentLanguages} from '#/state/preferences/languages'
 import {type FeedParams} from '#/state/queries/post-feed'
+import {type SessionAgent} from '#/state/session'
 import {FeedTuner} from '../feed-manip'
 import {type FeedTunerFn} from '../feed-manip'
 import {
@@ -24,7 +21,7 @@ const POST_AGE_CUTOFF = 60e3 * 60 * 24 // 24hours
 
 export class MergeFeedAPI implements FeedAPI {
   userInterests?: string
-  agent: AtpAgent
+  agent: SessionAgent
   params: FeedParams
   feedTuners: FeedTunerFn[]
   following: MergeFeedSource_Following
@@ -39,7 +36,7 @@ export class MergeFeedAPI implements FeedAPI {
     feedTuners,
     userInterests,
   }: {
-    agent: AtpAgent
+    agent: SessionAgent
     feedParams: FeedParams
     feedTuners: FeedTunerFn[]
     userInterests?: string
@@ -175,7 +172,7 @@ export class MergeFeedAPI implements FeedAPI {
 }
 
 class MergeFeedSource {
-  agent: AtpAgent
+  agent: SessionAgent
   feedTuners: FeedTunerFn[]
   sourceInfo: ReasonFeedSource | undefined
   cursor: string | undefined = undefined
@@ -186,7 +183,7 @@ class MergeFeedSource {
     agent,
     feedTuners,
   }: {
-    agent: AtpAgent
+    agent: SessionAgent
     feedTuners: FeedTunerFn[]
   }) {
     this.agent = agent
@@ -253,7 +250,7 @@ class MergeFeedSource_Following extends MergeFeedSource {
 }
 
 class MergeFeedSource_Custom extends MergeFeedSource {
-  agent: AtpAgent
+  agent: SessionAgent
   minDate: Date
   feedUri: string
   userInterests?: string
@@ -264,7 +261,7 @@ class MergeFeedSource_Custom extends MergeFeedSource {
     feedTuners,
     userInterests,
   }: {
-    agent: AtpAgent
+    agent: SessionAgent
     feedUri: string
     feedTuners: FeedTunerFn[]
     userInterests?: string