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>

custom_components/heating_mpc/strings.json

@@ -56,6 +56,13 @@
   "options": {
     "step": {
       "init": {
+        "title": "Heating MPC",
+        "menu_options": {
+          "settings": "Settings",
+          "reset_model": "Reset learned model"
+        }
+      },
+      "settings": {
         "title": "Heating MPC options",
         "description": "Change room sensors and controller settings. This integration remains shadow-only.",
         "data": {
@@ -83,10 +90,17 @@
           "window_open_minutes": "Forecasts assume an open window closes after this many more minutes, then the room recovers.",
           "recovery_minutes": "Time constant of the air warming back towards the walls' temperature.",
           "ventilation_wind": "Needs wind sources; direction also needs wind direction sources.",
-          "ventilation_gust": "Adds a term for gusts above the mean wind. Keep it only if Forecast Error improves.",
+          "ventilation_gust": "Adds a term for gusts above the mean wind. Keep it only if Model Error improves.",
           "ventilation_cross": "Adds a term for windows open in several zones at once. Needs windows in two or more zones."
         }
       },
+      "reset_model": {
+        "title": "Reset learned model",
+        "description": "Forgets everything the model has learned: every zone's thermal coefficients (also those kept for removed zones), their confidence and sample counts, and the Model Error and Forecast Error statistics.\n\nKept: zones, sensors and weights, heat sources, windows, weather sources and all settings, plus the heat sources' baselines and the window event log.\n\nThe integration restarts and learns from the beginning: the first sample after about 30 minutes, forecasts after a day or more. This cannot be undone. The boiler and the thermostat are not affected.",
+        "data": {
+          "confirm_reset": "Yes, forget the learned model"
+        }
+      },
       "weather": {
         "title": "Weather source priority",
         "description": "Choose as many sensors per metric as needed and arrange them in priority order. If the preferred source is unavailable, the next one is used automatically. Outdoor temperature is mandatory; wind and cloud coverage are diagnostic-only in this version.",
@@ -113,6 +127,10 @@
     },
     "error": {
       "invalid_weather": "Select at least one outdoor temperature sensor, distinct from room sensors."
+    },
+    "abort": {
+      "model_reset": "The learned model was reset. Learning starts again from the beginning.",
+      "model_not_reset": "Nothing was changed: the reset was not confirmed."
     }
   },
   "entity": {