Why: entering the forced-change gate with an API-key credential always
fails 401 (passwords are session-owned), and the gate mapped every 401
to "Incorrect username or password", masking the real reason and hiding
the self-service exit; admins got locked out before reaching user
management.
Evidence: npx vitest run green (20 files / 93 tests incl. new
test/loginpage.test.ts); tsc -b and check-knip green.
Impact: App boot routes key+mustChange to the login page (key cleared);
the API-key tab advises password login for must-change accounts; the
gate maps backend error strings to distinct actionable messages; api.me
type gains authVia.
Refs: Dev task feature/admin-auth-gate-fix.
weichen
dc18d6c747