Treat window states unknown at startup as unknown, and continue across restarts

Reproduced: with a window sensor already unavailable at startup, the
forecast assumed the window closed, exactly as for a window last seen
closed, and the first reading of an already open window was logged as a
confirmed opening.

- An opening or closing is confirmed only when witnessed: the previous
  reading was the other state with no unknown period between. A first
  reading, or a change across an outage or restart, is unconfirmed.
- Last known states, open events and recovery are saved (also whenever a
  window's state changes) and restored as unknown until the sensor
  reports; saved state for another sensor or polarity is ignored. Downtime
  counts as unknown time of an interrupted event.
- Forecast assumption per window: observed; last seen open, assumed open
  only until the configured open time after it was last seen (never
  renewed); last seen closed or never observed, no ventilation but marked
  uncertain. Status shows each window's assumption; zone forecasts list
  their uncertain windows.
- Events report a duration only when both ends are confirmed, otherwise a
  minimum (and a maximum when the opening was seen).

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

custom_components/heating_mpc/sensor.py

@@ -103,6 +103,8 @@ class MPCRoomPrediction(CoordinatorEntity, SensorEntity):
             "forecast_15min": trajectory or None,
             "plan_15min": data.get("plan_15min"),
             "basis": "proposed MPC plan; counterfactual while Generic Thermostat controls the relay",
+            # Windows with an unknown state: the forecast assumes their state (see Status).
+            "uncertain_windows": details.get("uncertain_windows") or [],
             "model_in_use": details.get("model_in_use"),
             "contributions_c_per_h": details.get("contributions_c_per_h"),
             "coefficients": details.get("coefficients"),