Photon now allowlists registered device clients on the device-code
endpoint; the old client_id "hermes-agent" is rejected with
400 invalid_client, breaking the entire login flow. Switch to Photon's
published "photon-cli" device client and send the standard scope.
Also validate the device-flow token against /api/auth/get-session and
/api/projects/ before persisting it, and extract token candidates from
every response shape Photon has used (access_token, accessToken,
data.*, set-auth-token header) so a token that authenticates the
session lookup but is rejected by the project API fails loudly at
login instead of 404ing downstream.
Verified live: request_device_code() now returns 200 + a valid
user_code where "hermes-agent" returned 400 invalid_client.
Salvaged from #34467 by @yanxue06.
37561c214b