fix(plant): alert hygiene — watchdog gate, trend smoothing, UPS [#344]

Three live-fire defects: unconditional 30-min watchdog page, tsys6 flap
false-positive, Tripp Lite runtime-low gap. TDD: 4 new regression tests.
On-box ha core check passed before commit.

Meat + verification: https://projects.knownelement.com/issues/344#note-4966

packages/plant_snmp.yaml

@@ -543,26 +543,56 @@ sensor:
     unique_id: pfv_garage_pdu_energy
 
 # --- Rate-of-change early warning (#682): +10°F/15min = AC trouble [#344] ---
+# DRAC sensors quantize to whole °C and FLAP ~1.8°F between polls; raw-fed
+# trend sensors false-tripped TEMP RISING FAST (2026-09-06 05:02 CDT, tsys6).
+# Trend inputs are 5-min time-weighted moving averages — real climbs survive
+# the smoothing, quantization flapping does not.
+filter:
+  - platform: time_simple_moving_average
+    name: "PFV tsys1 rack temperature smoothed"
+    entity_id: sensor.pfv_tsys1_rack_temperature
+    window: "00:05:00"
+    precision: 2
+    unique_id: pfv_tsys1_rack_temperature_smoothed
+  - platform: time_simple_moving_average
+    name: "PFV tsys6 DRAC ambient smoothed"
+    entity_id: sensor.pfv_tsys6_drac_ambient
+    window: "00:05:00"
+    precision: 2
+    unique_id: pfv_tsys6_drac_ambient_smoothed
+  - platform: time_simple_moving_average
+    name: "PFV tsys7 DRAC inlet smoothed"
+    entity_id: sensor.pfv_tsys7_drac_inlet
+    window: "00:05:00"
+    precision: 2
+    unique_id: pfv_tsys7_drac_inlet_smoothed
+  - platform: time_simple_moving_average
+    name: "PFV garage temperature smoothed"
+    entity_id: sensor.pfv_garage_temperature
+    window: "00:05:00"
+    precision: 2
+    unique_id: pfv_garage_temperature_smoothed
+
 binary_sensor:
   - platform: trend
     sensors:
       server_room_temp_rising:
-        entity_id: sensor.pfv_tsys1_rack_temperature
+        entity_id: sensor.pfv_tsys1_rack_temperature_smoothed
         sample_duration: 900
         min_gradient: 0.011
         unique_id: trend_server_room_rising
       tsys6_ambient_rising:
-        entity_id: sensor.pfv_tsys6_drac_ambient
+        entity_id: sensor.pfv_tsys6_drac_ambient_smoothed
         sample_duration: 900
         min_gradient: 0.011
         unique_id: trend_tsys6_ambient_rising
       tsys7_inlet_rising:
-        entity_id: sensor.pfv_tsys7_drac_inlet
+        entity_id: sensor.pfv_tsys7_drac_inlet_smoothed
         sample_duration: 900
         min_gradient: 0.011
         unique_id: trend_tsys7_inlet_rising
       garage_temp_rising:
-        entity_id: sensor.pfv_garage_temperature
+        entity_id: sensor.pfv_garage_temperature_smoothed
         sample_duration: 900
         min_gradient: 0.011
         unique_id: trend_garage_rising