In profile mode, _load_provider_state previously returned None when a
provider was absent from the profile's auth.json — even if the user had
authenticated at the global root. This broke runtime credential resolvers
that read state directly (resolve_nous_access_token,
resolve_nous_runtime_credentials), causing profiles without their own
nous login to fail with 'Hermes is not logged into Nous Portal' despite
a valid global session.
Push the existing read-only global fallback (already used by
get_provider_auth_state and read_credential_pool) into _load_provider_state
so every caller benefits, and simplify get_provider_auth_state into a thin
wrapper. Writes still target the profile only — profile state continues to
shadow global state on the next read after a per-profile login. Behavior in
classic (non-profile) mode is unchanged because _load_global_auth_store
returns an empty dict.
Adds 5 tests covering the new contract on _load_provider_state directly.
Existing 770 auth/credential/nous tests still pass.
