POST /auth/request-access had no caller left: the login page's form was
gone, and registration and a refused Google sign-in already land in the
same admin approval. A third public write path with no protection of
its own (owner decision, E34).
Its one guard moves to where every path passes: upsert_pending_invite no
longer opens a pending row for an address the env already lets in. The
registration path lacked it — registering b.ob@gmail.com beside an
env-granted bob@gmail.com opened a pending row, and is_allowed answers
from the invite rows once any exist, so the real owner was locked out.
The tests that drove the endpoint now drive registration or the shared
function.