Fan floors from the measurement; a hunt is measured, not judged

forgectrl pin 47e4256: the airflow floors set from the bench measurement
(exhaust 6400, intake 2290, air assist 6000 rpm, purge current 300, grace
15 s) and the operating-point rule: a fan is judged while the laser is
armed, when a job's profile may raise it but never lower it below the run
duty, or whenever it is commanded at the run duty; the service's hunts,
sent with the extraction fans off, are measured and published unjudged.

Catalog: cloud.mode-switch now waits out the connect-time hunt sampling
/cool/status and requires no AIRFLOW, the exhaust row unjudged and the
exhaust actually off; its covers gain forgectrl src/cool.* and
src/airflow.*. cooling.fan-gate-trips uses an 8 s test grace (the
intakes take 7 s to 90 percent and tripped under the old 2 s at the new
floor) and its off leg waits for the row state as well as gates_off.
fan_floor_measure.py names a reply that is not JSON and calls the purge
readings idle and run (the pump is always on).

Docs: COOLING 3a and the settings table, BRINGUP item 19 and a facts-bank
entry with the measured fan speeds, the bench README, and a CAMPAIGN-LOG
entry for the measurement, the two status-document finds, the hunt find
and the hot-deployed bench runs of both tests.

forgetest/tests/test_cooling_suite.py

@@ -498,7 +498,7 @@ class FanGateTests(unittest.TestCase):
         self.assertEqual(ev["exhaust_off"]["cool"]["gates_off"], ["exhaust"])
         self.assertTrue(all(g["state"] == "ok" for g in ev["restored"].values()))
         posts = self.settings_posts()
-        self.assertEqual(posts[0], {"cool_tach_exhaust_min_rpm": "20000.0", "cool_fan_grace_s": "2"})
+        self.assertEqual(posts[0], {"cool_tach_exhaust_min_rpm": "20000.0", "cool_fan_grace_s": "8"})
         self.assertEqual(posts[-1], {"cool_tach_exhaust_min_rpm": "", "cool_purge_min_current": "",
                                      "cool_fan_grace_s": ""})
         self.assertEqual(self.grbl.commands.count("M8"), 4)