Outlook to Live, humidity calibration, Models tab rebuilt without scrollers

Seven day outlook moves from History to Live, which now runs four rows.
Conditions ahead tightened so the Live column no longer needs a scroller.

Adds HumidityCompensator: an additive RH offset estimated by one-step RLS from
a trusted hygrometer, clamped to +/-35%, persisted, exposed at
POST /api/calibrate/humidity and on the renamed Models and calibration tab.

It also implements the psychrometric term (RH moved from element temperature
onto air temperature via conserved vapour pressure) but leaves it OFF by
default. The thermal argument predicts a hot element reads low; measured
against a reference hygrometer this board read 75.4% where the truth was
50.4%, so it reads HIGH and that correction would push it the wrong way. When
the flag is enabled, simulate.py applies the exact inverse, per the
simulator/compensator trap in DESIGN.md section 2.

Models pane rebuilt: the scorecard is one column per target so all 18 heads
are visible, and no panel on the tab uses an internal scroller. Verified in
Chromium at 1600x900: Live, History and Models all report zero scrollbars,
zero clipping, no page scroll, zero console errors. Backtest is numerically
identical to the previous commit, confirming the humidity work is a no-op
while the flag is off.

docs/DESIGN.md

@@ -99,6 +99,27 @@ exact inverse:** `T_raw = (T + k·T_cpu)/(1 + k)`. Generating the bias as
 1.2 °C of phantom noise floor that caps every skill score. This has already
 happened once.
 
+### Humidity compensation
+
+`HumidityCompensator` carries an additive `offset` on relative humidity,
+estimated from a trusted hygrometer by the same one-step RLS used for `k`, with
+the regressor fixed at 1 so repeated calibrations converge to a weighted mean.
+Clamped to +/-35% for the same reason `k` is clamped.
+
+It also implements a psychrometric term, moving RH from the element's
+temperature onto the compensated air temperature through conserved vapour
+pressure, `RH_true = RH_sensor * es(T_sensor) / es(T_true)`. That term is
+**off by default**, and the reason is worth recording. The thermal argument
+predicts a hot element reads LOW. Measured against a reference hygrometer this
+board read 75.4% where the truth was 50.4%, so it reads HIGH by 25 points, and
+the correction would have pushed it further the wrong way. The dominant error on
+this hardware is additive element bias, not a thermal gradient.
+
+If you enable `sensor.hum_psychrometric`, `scripts/simulate.py` applies the exact
+inverse when generating synthetic humidity. It has to: the same
+simulator/compensator algebra trap described above for temperature applies here,
+and getting it wrong bakes in a bias no calibration can remove.
+
 ### The Kalman bank
 
 One constant-velocity filter per signal. State `x = [level, rate]`, standard
@@ -302,7 +323,8 @@ consecutive readings are the only tell.
 
 | Symptom | Knob | Direction |
 |---|---|---|
-| Temperature reads consistently high | Calibrate from the Models tab, or `sensor.cpu_heat_k` | Raise |
+| Temperature reads consistently high | Calibrate from the Models and calibration tab, or `sensor.cpu_heat_k` | Raise |
+| Humidity reads consistently off | Calibrate against a reference hygrometer, or `sensor.hum_offset` | Either |
 | Readings over-smoothed, lag real change | `sensor.kalman_q_temp` | Raise |
 | Rates look noisy | `sensor.kalman_q_*` down, or `kalman_r_*` up | |
 | NIS persistently much above 1 | Filter too confident, raise `q` | Raise |