SAFETY-118: read the peak forecast in its own unit

peak_forecast_entity is read through pv.watts() by its unit_of_measurement;
the abs(raw) < 50 size rule is gone. No unit or a non-power unit means the
forecast is not used, with one warning per cause. The validator no longer
claims a kW sensor is taken as watts for this entity.

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

goodwe_controller/DOCS.md

@@ -210,7 +210,7 @@ The label and description each setting shows on the Configuration tab, in tab or
 | Limits | Battery cut-out level (%) | `bms_soc_floor` | The level where the battery's own management system stops giving power. Read it off your battery rather than copying a figure. |
 | Limits | Peak limit (W) | `peak_cap_w` | Your own number: the 15-minute average power the add-on keeps the grid under. Take it from your grid contract. |
 | Limits | Margin below the peak limit (W) | `peak_margin_w` | The add-on aims this much below the peak limit, so a 15-minute period that ends a little high still stays under it. |
-| Limits | 15-minute demand forecast entity (W) | `peak_forecast_entity` | Optional. A forecast of this 15-minute period's average power. Leave it empty and there is no peak limit. |
+| Limits | 15-minute demand forecast entity (W) | `peak_forecast_entity` | Optional. A forecast of this 15-minute period's average power, in W or kW. With no power unit it is not used. Leave it empty and there is no peak limit. |
 | Limits | Peak reserve (%) | `peak_soc_floor` | Peak limiting will not draw the battery below this level, but ordinary use can. Derived value, leave it unchanged. |
 | Tariff | Dynamic price source | `price_provider` | Where prices come from. Choosing a source starts the price fetch, even with trading off. |
 | Tariff | Supplier markup (EUR/kWh) | `price_markup_eur_kwh` | Your supplier's margin. It is added only when the price source does not already include it. |
@@ -1697,7 +1697,7 @@ DECISIONS/MAINT-13-full-pack-is-complete.md.
 
 | option | meaning |
 |---|---|
-| `peak_forecast_entity` | Quarter-hour demand forecast, for capacity-tariff markets. Empty = no cap |
+| `peak_forecast_entity` | Quarter-hour demand forecast, for capacity-tariff markets. Read in its own unit (W, kW or any power unit). No unit, or a unit that is not power, means it is not used, as if empty (SAFETY-118). Empty = no cap |
 | `peak_cap_w` | The site's capacity-tariff target |
 | `peak_margin_w` (50) | Watts the peak guard aims under `peak_cap_w` (SAFETY-79). Reports and the bill use `peak_cap_w` itself |
 | `peak_soc_floor` (20) | **The percent below which the capacity-peak guard will not discharge the battery.** ⚠️ It bounds **the peak guard only** — it is **not a pack-wide reserve**, and ordinary self-consumption discharges straight past it (SAFETY-25, see below). Not optional and not the same thing as `maintenance_soc_floor` |