Show each sensor's longest report gap; stop recording volatile attributes

Choosing room and weather freshness limits required knowing how long
each sensor normally goes without reporting, which HA does not show.
Add max_age_seconds_24h to every source in input_quality: the largest
report age seen at polls over the last 24 hours (hourly buckets, reset
on reload, underestimates by up to one poll interval).

input_quality and weather_comparison change every poll, so the Recorder
stored a new attribute row every five minutes. Mark them unrecorded;
they remain visible on the Status entity. Model coefficients and other
attributes are still recorded.

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

custom_components/heating_mpc/data_quality.py

@@ -1,6 +1,7 @@
 """Pure timestamp validation for reported sensor snapshots."""
 from __future__ import annotations
 
+from collections import deque
 from datetime import datetime
 from math import isfinite
 
@@ -16,3 +17,23 @@ def freshness(reported: datetime | None, now: datetime, max_age_seconds: float)
         return {"status": "future_timestamp", "age_seconds": round(age, 1)}
     return {"status": "stale" if age > max_age_seconds else "valid",
             "age_seconds": round(age, 1)}
+
+
+class ReportAgeHistory:
+    """Largest report age seen at polls per entity over the last 24 hours.
+
+    Helps choose freshness limits: a limit below a sensor's normal maximum
+    marks it stale during ordinary operation. Hourly buckets keep memory bounded.
+    """
+
+    def __init__(self) -> None:
+        self._buckets: dict[str, deque[list[float]]] = {}
+
+    def observe(self, entity_id: str, now: datetime, age_seconds: float) -> float:
+        hour = now.timestamp() // 3600
+        buckets = self._buckets.setdefault(entity_id, deque(maxlen=25))
+        if buckets and buckets[-1][0] == hour:
+            buckets[-1][1] = max(buckets[-1][1], age_seconds)
+        else:
+            buckets.append([hour, age_seconds])
+        return max(age for start, age in buckets if hour - 24 < start <= hour)