Prove the dose curve and the recorder; document S-means-light

The stream harness gains rule 19: with the bench-default curve in force
a ladder of S rungs renders the curve's densities exactly (half light
lands near 80 percent density), monotonic, floored and ceiled by
$35/$36; every other session pins laser_dose_curve = off so its
S-to-level arithmetic stays exact, and the arm-report checks carry the
curve name. The lifecycle harness asserts the published state file
names the curve in force. The catalog's forgectrl.panel-serves asserts
the curve field in the grbl report, /curve/status and the ladder
G-code, and its covers name the recorder.

BRINGUP describes S-commands-light through the measured curve and the
owner recorder; the MOTION table gains laser_dose_curve; LIGHTBURN
tells the operator power now means light and how to record their own
tube's curve from the panel.

scripts/bench/laser_lifecycle_test.py

@@ -296,6 +296,8 @@ def test_status_files():
         assert '"armed":false' in st, "armed before any job: %r" % st
         assert '"model":"density"' in st and '"floor_pct":10' in st, \
             "model/floor missing (the floor must be derived from boot): %r" % st
+        assert '"curve":"bench-default"' in st, \
+            "the curve in force is not published: %r" % st
         assert '"modals":"[GC:' in st, "modal report missing: %r" % st
         ts0 = float(st.split('"ts_mono":')[1].split(',')[0])