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.

.env.example

@@ -53,6 +53,9 @@ NTFY_TOKEN=
 PUBLIC_URL=https://water.buildfor.life/
 # Report RID lagging this many hours while ThaiWater telemetry is current (0 = never)
 RID_STALE_ALERT_HOURS=18
+# RID publishes nothing overnight: from 21:00 until this hour a quiet river's
+# feed is not reported stale (0 = off; docs/NOTIFICATIONS.md)
+FEED_NIGHT_UNTIL_HOUR=9
 # Matrix room for a team: the same transitions (docs/MATRIX_QUICK_START.md);
 # off while token or room is empty
 MATRIX_HOMESERVER=https://matrix.org