repoint the last AtpAgent statics and drop the dead conversions

Five sites read `AtpAgent.appLabelers`, which the previous commit stopped
populating - a silent regression, since an empty static reads as "no
authorities" rather than failing. All now read `Client.appLabelers`, the static
that is actually configured:

- `lib/moderation.ts`'s `isAppLabeler`, which decides whether a labeler is
  non-removable in the UI;
- `preferences/moderation.ts`'s `useMyLabelersQuery`, which seeds the labeler
  list with the app authorities;
- `feed/custom.ts`'s hand-rolled logged-out `getFeed`, which reproduces the
  header lex would have emitted because the request bypasses the client.

`sessionAccountToSession` (the `AtpSessionData` conversion) had no callers left
once the bridge agent went, and the age assurance config read - the one
standalone `new AtpAgent` the age assurance slice deliberately left behind -
moves to the public appview client, which is what it was approximating.

That is the last `AtpAgent` in src. What remains of `@atproto/api` in the
session layer is types and `BSKY_LABELER_DID`, which S4d owns.

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

src/state/session/session-data.ts

@@ -1,4 +1,3 @@
-import {type AtpSessionData} from '@atproto/api'
 import {getPdsEndpoint, isValidDidDoc} from '@atproto/common-web'
 import {type SessionData} from '@atproto/lex-password-session'
 import {jwtDecode} from 'jwt-decode'
@@ -81,27 +80,6 @@ export function sessionAccountToSessionData(
   }
 }
 
-/** Convert a persisted account into data suitable for `AtpAgent`. */
-export function sessionAccountToSession(
-  account: SessionAccount,
-): AtpSessionData {
-  return {
-    // Sorted in the same property order as when returned by BskyAgent (alphabetical).
-    accessJwt: account.accessJwt ?? '',
-    did: account.did,
-    email: account.email,
-    emailAuthFactor: account.emailAuthFactor,
-    emailConfirmed: account.emailConfirmed,
-    handle: account.handle,
-    refreshJwt: account.refreshJwt ?? '',
-    /**
-     * @see https://github.com/bluesky-social/atproto/blob/c5d36d5ba2a2c2a5c4f366a5621c06a5608e361e/packages/api/src/agent.ts#L188
-     */
-    active: account.active ?? true,
-    status: account.status,
-  }
-}
-
 export function isSessionExpired(account: SessionAccount) {
   return account.accessJwt ? isJwtExpired(account.accessJwt) : true
 }