hold the three clients in the bundle and delete the bridge agent

The bundle becomes `{session, appviewClient, pdsClient, chatClient, service}`
and the hooks read those fields directly, so `useAgent` and the three
`agentTo*Client` memo maps go with the agent. The WeakMaps existed only because
clients were derived from a long-lived agent; a bundle that HOLDS its clients
gets identity stability for free.

The clients are now the sole producers of their own headers, which is what lets
`bridge-agent.ts` (442 lines) and `agent.ts` go:

- the appview client passes BLUESKY_PROXY_HEADER as its `service`, so it emits
  atproto-proxy itself rather than inheriting it from a configureProxy call
  sequenced after the PDS-targeting setup;
- labeler subscriptions go on the appview instance via `setLabelers`, and the
  global `;redact` authorities come from the `Client` static alone. Both halves
  of the double-emit hazard the previous slice documented are closed by there
  being one producer instead of two, so the appview client no longer suppresses
  `appLabelers` - only the PDS and chat clients do, because those services take
  no moderation authorities at all;
- `configureGlobalAppLabelers` drops its `AtpAgent.configure` half.

PDS routing for the pre-didDoc window is `routeSessionToPds`, a 10-line shim
replacing the manager's dispatchUrl/extractPdsUrl/identity-cache apparatus.
`PasswordSession` resolves each request against `extractPdsUrl(didDoc) ??
service`, so an entryway account with no didDoc yet - the synchronous resume
fast path, i.e. the common cold start - would send every request to the
entryway. The shim absolutizes against the stored url first, which survives
`new URL(path, base)` untouched. It pins that url for the bundle's lifetime
where the manager would have preferred a later didDoc endpoint; that only
differs if the account's PDS moved, and the next cold start pins the new one.
Four cases in clients-test cover this, including the two the old suite could
not express (pinned-vs-didDoc precedence, and didDoc routing with nothing
pinned).

`createPublicSessionBundle` now runs `configureModerationForGuest` itself. That
is a behavior fix, not a refactor: it populates the `Client.appLabelers` static
the public appview client reads, and with no agent left to stamp the header a
logged-out read would otherwise carry no moderation authorities.

finishPreparation, the kill-switch disposal, the redacted logging, refreshSession
and the expiry-rescue path are unchanged - only how the bundle is constructed
moved. Disposal is now just the hook kill: the clients hold no state, and every
request they make goes through the session's injected fetch.

bridge-agent-test.ts is deleted with its subject. clients-test.ts is rewritten
against session-built clients, keeping every header canary (exactly-once on the
appview, none on pds/chat, exact proxy values, the throwing client's cause
chain). The three provider suites and session-core-test are adapted in place -
their constructions change, their assertions do not.

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

src/lib/constants.ts

@@ -2,7 +2,6 @@ import {type Insets, Platform} from 'react-native'
 import {type AppBskyActorDefs, BSKY_LABELER_DID} from '@atproto/api'
 import {type Service} from '@atproto/lex'
 
-import {type ProxyHeaderValue} from '#/state/session/agent'
 import {BLUESKY_PROXY_DID, CHAT_PROXY_DID, IS_DEV} from '#/env'
 
 export const LOCAL_DEV_SERVICE =
@@ -241,7 +240,7 @@ export const DEV_ENV_APPVIEW_DID = `did:plc:dw4kbjf5mn7nhenabiqpkyh3` // always
 export const BLUESKY_PROXY_HEADER = {
   value: `${BLUESKY_PROXY_DID}#bsky_appview`,
   get() {
-    return this.value as ProxyHeaderValue
+    return this.value as Service
   },
   set(value: string) {
     this.value = value