monitoring: TechnitiumZoneCountMismatch — compare replicas only, exclude primary

Primary has only the Primary-type zones it owns (10). Replicas have those
+ built-in zones (localhost, in-addr.arpa reverse, etc.), so their count
(14) can never match primary. Alert expr compared max-min across all
instances, making it chronically firing.

Fix: instance!="primary" filter. The real signal this alert wants is
"did one replica drift from the others" — replica-to-replica comparison
captures that; primary was never comparable.

stacks/monitoring/modules/monitoring/prometheus_chart_values.tpl

@@ -1980,7 +1980,7 @@ serverFiles:
             annotations:
               summary: "Technitium zone-sync has not run successfully in >1h (last: {{ $value | humanizeDuration }} ago)"
           - alert: TechnitiumZoneCountMismatch
-            expr: (max(technitium_zone_count) - min(technitium_zone_count)) > 0
+            expr: (max(technitium_zone_count{instance!="primary"}) - min(technitium_zone_count{instance!="primary"})) > 0
             for: 15m
             labels:
               severity: warning