fix(gate): no admission lock in a tree without .mam; MAM_UPDATE_MONITOR_STOP_S in the knob table (Issue #72)

mam_update_admit created .mam/ to hold its lock, so a checkout running its
own run_loop.sh got a .mam (test_loop_marker_isolation L1, test_issue17 W1).
A tree without .mam is not an installed workspace, the only kind the update
runs in, so the gate admits there without a lock. The update's monitor-stop
wait is a normalised integer knob and is listed in INT_KNOBS
(test_issue26_ints B5).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/test_issue26_ints.py

@@ -59,6 +59,8 @@ INT_KNOBS = {
     # once) and the wrapper's registry wait (0: decide at once - clear or busy)
     "MAM_ONBOARD_WAIT_S": (1, "600"),
     "MAM_DISPATCH_WAIT_S": (0, "600"),
+    # Issue #72: how long the update waits for the monitor to stop after SIGTERM
+    "MAM_UPDATE_MONITOR_STOP_S": (1, "30"),
     # delegate_wait_started's ack_s (MAM_ONBOARD_ACK_S / DELEGATE_JOB_ACK_S via create_session.sh)
     "delegate_wait_started:ack_s": (0, "180"),
     # wrapper flags