Send people of a depot on single sign-on to their identity provider when they try a password

Brakeline's nine depots are on Entra ID since March, but people still type their email and old password on our sign-in page. Their password stopped working when their depot switched, so they get "Wrong email or password" and ring support (four calls last week).

Acceptance criteria

• When the email belongs to a person whose home depot is on single sign-on, the password step is skipped and they go straight to their identity provider.
• The page says why: "Your depot signs in with your company account."
• People on phone codes, and depots still on passwords, see nothing new.