Add Reset learned model to Configure

Configure now opens a menu: Settings (the previous form) or Reset learned
model. After an explicit confirmation the entry is unloaded, the learned
parts of the stored model (zone, extended and ventilation coefficients,
models kept for removed zones, Model Error and Forecast Error statistics,
fingerprints) are removed under the storage lock, and the entry is set up
again. Configuration, heat-source baselines and the window event log are
kept, and model_changes records the reset. Unloading first means no update
still running can write the old model back. English and Romanian strings;
the gust hint now refers to Model Error.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -23,8 +23,8 @@ On Home Assistant 2026.3 or newer the integration shows its own icon (a radiator
 
 On **Settings → Devices & services → Heating MPC**, the buttons **Add zone**, **Add
 heat source** and **Add window** create items that can each be edited or deleted
-later. **Configure** holds everything else: thermostat, relay, weather sources,
-report-age limits, MPC settings and model options.
+later. **Configure** offers **Settings** (thermostat, relay, weather sources,
+report-age limits, MPC settings and model options) and **Reset learned model**.
 
 **Zones** are rooms or areas. Each has a name, one or more temperature sensors, a
 comfort weight (how much the zone matters to the MPC), an optional target offset
@@ -45,6 +45,15 @@ or the recovery time resets only the coefficients that depend on it. Comfort
 weight, target offset and names never touch the model. Each recalibration is
 listed in the Status attribute `model_changes`.
 
+**Reset learned model** (in **Configure**, after ticking the confirmation) forgets
+everything learned: every zone's coefficients, including those kept for removed
+zones, with their confidence and sample counts, and the Model Error and Forecast
+Error statistics. Zones, sensors, weights, heat sources, windows, weather sources
+and settings stay as they are, and so do the heat sources' baselines and the window
+event log. The integration restarts and learns from the beginning (first sample
+after about 30 minutes, *Ready* after a day or more); `model_changes` records the
+reset. It never touches the boiler or the thermostat.
+
 **Heat sources** are equipment whose electricity ends up as heat in a zone, such as
 a UPS feeding computers. Settings: an active-power sensor (W or kW; VA and % are
 rejected), the zone, the share of the power that becomes heat there (1.0 by