auth: rename session identifiers to AuthSession forms
Commit

Apply the Auth-prefix renames across the moved files and call sites: api.Session -> AuthSession, ListSessions -> ListAuthSessions, etc., plus cli helpers (newAuthSessionsClient, defaultListAuthSessions, revokeAllAuthSessions, ...). JSON wire key stays "tokens".
Co-Authored-By: Claude Opus 4.8 (1M context) noreply@anthropic.com Entire-Checkpoint: c6c44b763a39
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