…es (#1407)

* fix: share one exchanged WIF credential across spawned Claude processes

GitHub OIDC tokens are single-use at the Anthropic token-exchange
endpoint (the same jti cannot be exchanged twice). With plugins
configured, the action spawns several short-lived claude processes
(plugin marketplace add, one plugin install per plugin, then the main
query). Each resolved federation from bare env vars and exchanged the
same identity-token file independently: the first exchange succeeded
and every later process got 401 (jti_reused), which the main query
retried for ~3 minutes before failing the job.

The SDK only enables its on-disk credentials cache when federation is
loaded from a profile config file, not from bare env vars. Write a
profile pointing at the identity-token file and select it via
ANTHROPIC_CONFIG_DIR / ANTHROPIC_PROFILE so the first process exchanges
once and the rest reuse the cached access token. The env vars are kept
as a fallback for CLIs that predate profile support.

* fix: scope the WIF credential cache per federation config

Address review feedback on the shared-credentials-cache fix:

- Embed a fingerprint of the federation inputs (rule, org, service
  account, workspace, base URL, scope) in the config dir name. The SDK
  cache reuses a token on expires_at alone and RUNNER_TEMP is per-job,
  so a later step with different federation inputs would silently reuse
  the first step's token. service_account_id and scope are included
  beyond the reviewed list because both are sent in the exchange
  request body and change which credential is minted.
- Skip the action-managed profile with a warning when the operator has
  already set ANTHROPIC_CONFIG_DIR or ANTHROPIC_PROFILE.
- Shrink the profile to the minimal file-backed form; the CLI's bundled
  SDK gap-fills the federation fields from the env vars the action
  already exports (verified against the pinned 2.1.173 binary).
- Remove the token dir in stop() so the identity token and the cached
  exchanged credential don't outlive the step.
- Document that cache sharing relies on the plugin subprocesses
  spawning sequentially.