Leave out unusable rooms instead of pausing; add keep-last-value option

A single stale, unavailable, missing or invalid room sensor paused
learning and forecasts for every room. That is not acceptable once the
MPC may control heating.

Now such a room is left out: the weighted temperature, learning and the
optimizer use the remaining rooms with their weights re-normalized, and
a room learns only across poll pairs where it was usable at both ends.
Readiness considers only the rooms used. Everything pauses only when no
room is usable or a shared input (relay, thermostat, outdoor
temperature) is missing.

A new setup/Configure checkbox, room_stale_use_last_value (default off),
keeps using a stale room sensor's last value instead, for sensors that
report only on change. It never applies to unavailable or invalid
sensors, or to a sensor silent for more than 24 hours.

Status adds excluded_rooms, weight_coverage and a per-room "used" flag.
English and Romanian labels and help text added.

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

custom_components/heating_mpc/config_flow.py

@@ -9,7 +9,7 @@ from homeassistant.core import callback
 from homeassistant.helpers import selector
 
 from .const import (
-    CONF_ROOM_MAX_AGE, CONF_WEATHER_MAX_AGE,
+    CONF_ROOM_MAX_AGE, CONF_ROOM_STALE_KEEP, CONF_WEATHER_MAX_AGE,
     DOMAIN, CONF_CLIMATE, CONF_HEATER, CONF_OUTSIDE, CONF_ROOMS,
     CONF_WEIGHTS, CONF_HORIZON, CONF_MIN_ON, CONF_MIN_OFF,
     CONF_SWITCH_COST, CONF_HEAT_COST, CONF_BAND, DEFAULTS,
@@ -41,6 +41,8 @@ def _main_schema(config: dict[str, Any] | None = None, detailed: bool = False):
     for key in (CONF_ROOM_MAX_AGE, CONF_WEATHER_MAX_AGE):
         schema[vol.Required(key, default=data.get(key, DEFAULTS[key]))] = vol.All(
             vol.Coerce(int), vol.Range(min=5, max=1440))
+    schema[vol.Required(CONF_ROOM_STALE_KEEP, default=bool(
+        data.get(CONF_ROOM_STALE_KEEP, DEFAULTS[CONF_ROOM_STALE_KEEP])))] = selector.BooleanSelector()
     if detailed:
         for key, allowed in {
             CONF_HORIZON: vol.In([60, 90, 120, 150, 180]),