fix(notify): no "gauge feed stale" for RID's nightly pause on a quiet river

ping-status sent "gauge feed stale" around midnight and "feed recovered"
around 07:00 on each of the last three nights (ntfy and, since phase 3, the
Matrix room). RID publishes no hourly report overnight: the 21:00 reading is
the last until the 22:00..06:00 hours arrive together (06:35, 06:55, 07:22 on
2026-10-17/18/19). The ThaiWater overlay was meant to bridge that, but
ThaiWater's copies of the RID gauges come from the same feed with the same
delay (P.1's mirror still has no value for 22:00-00:00 this morning), so it
does not.

Between 21:00 and FEED_NIGHT_UNTIL_HOUR (default 9, 0 = off) the feed of a
quiet river is no longer reported stale; one still without new readings at
09:00 is. While a station is at warning/danger or the P.1 outlook is on, the
3 h rule holds all night. A feed already stale stays stale through the night
(no false "recovered"), and a real recovery is announced at any hour. The
replay of the Python notifier runs with the window off. Docs no longer claim
that ThaiWater keeps the feed current at night.

rust/README.md

@@ -62,9 +62,10 @@ readings and forecasts with `notification_state`.
   fails while it differs from Python; a change needs a rebuild.
 - **ntfy** topics, texts and hysteresis: [docs/NOTIFICATIONS.md](../docs/NOTIFICATIONS.md).
   For the stations whose ThaiWater twin is the same sensor, a reading newer
-  than RID's (RID lags 2-10 h at night) drives the level alerts, marked as
-  ThaiWater telemetry. "Gauge feed stale" means no source has a reading for
-  3 h; RID alone lagging is reported once after `RID_STALE_ALERT_HOURS`.
+  than RID's drives the level alerts, marked as ThaiWater telemetry. "Gauge
+  feed stale" means no source has a reading for 3 h, except during RID's
+  nightly pause (21:00 to `FEED_NIGHT_UNTIL_HOUR`, 9) while the river is
+  quiet; RID alone lagging is reported once after `RID_STALE_ALERT_HOURS`.
 - **Matrix** (`MATRIX_*`): the room gets the same transitions (per station,
   outlook, feed; not ntfy's per-topic summaries), each once, tracked under
   its own `matrix:` keys in `notification_state`, so a Matrix outage is