Merge PR #976: in-cluster app-health probes for navidrome and lidarr (REN-21)

Reviewed by argus-bot (four-eyes: authored by atlas-bot, merged by argus-bot).
One file, kubernetes/apps/monitoring-rules/probes-blackbox.yaml, additive only.
blackbox-http 17 -> 19 targets; other two Probe documents unchanged.
Revert: delete the added target lines and comment block (tested clean).
Do NOT use git revert -m 1 on this merge once #977 has landed -- the natural
conflict resolution silently removes the paperless probe too. See REN-22.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

kubernetes/apps/monitoring-rules/probes-blackbox.yaml

@@ -88,6 +88,35 @@ spec:
         # /ready answers 200 unauthenticated and is in this namespace, so the
         # same intra-namespace allowance the two above rely on covers it.
         - http://loki.monitoring.svc.cluster.local:3100/ready
+        # APP-HEALTH probes for the two gated navidrome-namespace apps. Same
+        # rule as the block above (monitoring-vantage-point-rule), but these
+        # are the first targets here that leave the monitoring namespace.
+        #
+        # Both sit entirely behind an Authentik outpost — navidrome.renner.uno
+        # on ak-outpost-navidrome-gate (navidrome/ingress.yaml:21),
+        # lidarr.renner.uno on ak-outpost-lidarr-gate
+        # (navidrome/lidarr.yaml:218) — so an EXTERNAL probe of either name
+        # measures the gate, not the app, and stays green while the app behind
+        # a live gate is dead. That external signal is still wanted, and REN-2
+        # adds it from UptimeRobot; these are the other half of the pair.
+        #
+        # NO CiliumNetworkPolicy change is needed, unlike what a reading of
+        # cnp-cross-namespace-allow-apps-gatus-to-monitored-services suggests.
+        # That gotcha is about `apps`, where GATUS runs; the influxdb
+        # allow-list it describes already contained `monitoring`. The
+        # navidrome baseline CNP likewise already admits the whole monitoring
+        # namespace on every port
+        # (infrastructure/network-policies/navidrome-ns.yaml:25-27), which is
+        # where blackbox-exporter runs. Nothing in the navidrome namespace is
+        # edited by this change.
+        #
+        # /ping on both: unauthenticated, and already the pods' own kubelet
+        # probe path (navidrome/deployment.yaml:61-74,
+        # navidrome/lidarr.yaml:114-127). For lidarr that it is ungated is
+        # proven independently of the gate — lidarr.yaml:29 curls /ping in a
+        # loop BEFORE it has read the API key out of config.xml.
+        - http://navidrome.navidrome.svc.cluster.local:80/ping
+        - http://lidarr.navidrome.svc.cluster.local:80/ping
 # WAN-path probes of the public edge BY PROXY IP. The name-based
 # home.renner.uno probe above resolves in-cluster (CoreDNS/k8s_gateway)
 # and never leaves the LAN — the vantage-point blind spot that let the