fix(test): arm smoke runtime cleanup at init, retire the daemon first

Review on #2199: cbm_test_runtime_init ran more than a hundred lines
before the only EXIT trap, so under `set -e` a failure in the fixture
mktemp or its cygpath conversion left the private root behind, and the
fixture trap ran smoke_rmtree ahead of the runtime cleanup.

Arm `trap 'cbm_test_runtime_cleanup "$BINARY"' EXIT` immediately after
a successful init, as soak-test.sh and memlab.sh do. The fixture trap
that replaces it now retires the private daemon first and removes the
fixtures second, so no earlier cleanup step stands between the exit and
the runtime cleanup; on Windows the retirement is also what unblocks
the fixture rm.

tests/test_smoke_runtime_isolation_contract.sh pins the early trap to
the window between the init call and the first fixture; the pin fails
against the previous head.

Part of #1696.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Signed-off-by: Anton Standrik <astandrik@yandex-team.ru>