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/const.py

@@ -12,6 +12,9 @@ CONF_SWITCH_COST = "switching_cost"
 CONF_HEAT_COST = "heating_cost"
 CONF_ROOM_MAX_AGE = "room_max_age_minutes"
 CONF_WEATHER_MAX_AGE = "weather_max_age_minutes"
+# Stale room sensors: False leaves them out (re-weighting the other rooms),
+# True keeps using their last value for sensors that report only on change.
+CONF_ROOM_STALE_KEEP = "room_stale_use_last_value"
 CONF_BAND = "comfort_band"
 
 # Each source list is ordered: first valid sensor wins; remaining are fallbacks.
@@ -32,6 +35,7 @@ WEATHER_EXTRA = ("humidity", "feels_like", "pressure", "visibility", "rain", "sn
 DEFAULTS = {
     CONF_ROOM_MAX_AGE: 30,
     CONF_WEATHER_MAX_AGE: 120,
+    CONF_ROOM_STALE_KEEP: False,
     CONF_HORIZON: 120,
     CONF_MIN_ON: 15,
     CONF_MIN_OFF: 10,
@@ -39,5 +43,7 @@ DEFAULTS = {
     CONF_HEAT_COST: 0.025,
     CONF_BAND: 0.15,
 }
+# A room sensor silent this long is treated as dead even when keeping last values.
+ROOM_STALE_KEEP_MAX_MINUTES = 24 * 60
 SAMPLE_MINUTES = 5
 BLOCK_MINUTES = 15