Prove the M101 dose-model switch; record the judged dose curves

The stream harness gains rules 18 to 21: the floor is derived from the
selected model's config key at the arm and a typed $35 is overwritten;
M101 switches the rendering exactly at the boundary in both directions
with no continuous FIRE at full duty across it; a refused switch (the
spindle on) leaves the stream unchanged, and the harness resyncs with
an empty line because the core skips G-code after an error until the
sender resyncs; M2 reverts a program-scoped switch and Q1 holds. The
analog sessions pin laser_floor_analog at the density floor so the
existing duty expectations stand, and the density ladder's unfloored
run moves from a chained $35 write to the laser_floor_density key.

The catalog's laser.power-floor becomes model-aware: it reads the
configured model and the floor keys from forgectrl, switches to the
configured model with M101 so the derivation runs without a fire, and
expects $35 to be that model's floor. The new laser.power-model-switch
switches to each model with the spindle off, checks the reported
message and $35 after each switch, and checks the M2 revert. The new
mswitch bench drill runs the switch on the machine in one armed run.

Docs follow: BRINGUP's Laser control section describes the switch, the
derived floors and the measured dose response of both models; the
MOTION settings table gains the five keys; LIGHTBURN gains a Power
models section and drops the stale 30 percent floor advice; SAFETY
names the switch's refusal rule; the CAMPAIGN-LOG records the judged
depth-witness runs of 2026-08-30 and the switch's host and bench proof.

docs/MOTION.md

@@ -426,6 +426,11 @@ only be changed while the machine is idle.
 | `lid_policy` | `cancel` | `cancel` = factory behavior; `hold` = stock Grbl door parking. |
 | `laser_button_timeout_s` | 300 | How long the machine waits at the button prompt. |
 | `laser_disarm_s` | 60 | Spindle-off grace before the armed window closes. |
+| `laser_power_model` | `density` | The boot-default dose model: `density` (full-power pulses, dose by pulse density) or `analog` (continuous beam, dose by PWM duty). A job overrides it with `M101 P0` / `M101 P1`. |
+| `laser_floor_density` | 10 | The S-range floor under density, percent of full; loaded into `$35` at every arm and switch. |
+| `laser_floor_analog` | 16 | The S-range floor under analog, percent duty (the duty the tube lases at); loaded into `$35` the same way. |
+| `laser_pulse_ticks` | 20 | Density base period in machine ticks (35.5 us each). |
+| `laser_pulse_min_ticks` | 3 | Shortest density pulse in ticks; below it a period is skipped and its debt carried. |
 | `rail_settle_s` | 2.5 | Motor-rail off period when a controller takes the device standalone. |
 | `cloud_pause_backtrack_ticks` | 2000 | Cloud pause: laser-off backtrack after the stop. |
 | `cloud_resume_lead_ticks` | 1950 | Cloud resume: laser-off lead before firing again. |