Every account helper in tests/play sets profiles.is_test right after the
account is made (guest or GoTrue admin), before it can queue, and fails
loudly when the marker did not stick.

tests/play/match-pool.mjs: two test accounts and two unmarked stand-ins for
real players, made with the admin API (no guest signups). In every public
queue, in a bucket the app never offers a real player where the game has
one, a test account is not seated with a real player waiting longer, by the
queue call or the status poll; two test accounts are seated together on both
paths; a real player searching passes a waiting test account; two real
players still pair; domino's public tables keep apart the same way; and a
player's own token cannot set is_test either way. Against the code before
the fix it fails 42 checks; after, 63 of 63 pass. Teardown is verified.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>