Replace shared redis-exporter VMPodScrape with per-app scrapes

Per review: drop the cross-namespace label-selector approach. Each app now
carries its own VMPodScrape next to its redis/valkey manifests, selecting on
the deployment's existing pod labels (mirroring the arrstack exportarr
pattern), so no opt-in monitoring.unkin.net/redis-exporter label is needed.

- Remove the monitoring.unkin.net/redis-exporter pod label from the
  artifactapi/authentik/litellm redis and gitea/netbox valkey deployments
- Delete apps/base/observability/vmpodscrape-redis.yaml
- Add a local-namespace VMPodScrape (port metrics, path /metrics) to
  artifactapi, authentik, litellm (app=redis), gitea (app=gitea-valkey),
  netbox (app=netbox-valkey), and jellyfin (valkey-operator node labels)

apps/base/observability/kustomization.yaml

@@ -9,5 +9,4 @@ resources:
   - gateway.yaml
   - httproute.yaml
   - vmpodscrape-cnpg.yaml
-  - vmpodscrape-redis.yaml
   - vmpodscrape-traefik.yaml

apps/base/observability/vmpodscrape-redis.yaml

@@ -1,40 +0,0 @@
----
-# Scrape metrics (:9121) from every redis/valkey pod carrying a redis_exporter
-# sidecar in any namespace. Raw redis/valkey Deployments opt in via the
-# monitoring.unkin.net/redis-exporter pod label. Picked up by the observability
-# VMAgent (selectAllByDefault).
-apiVersion: operator.victoriametrics.com/v1beta1
-kind: VMPodScrape
-metadata:
-  name: redis-exporters
-  namespace: observability
-spec:
-  namespaceSelector:
-    any: true
-  selector:
-    matchLabels:
-      monitoring.unkin.net/redis-exporter: "true"
-  podMetricsEndpoints:
-    - port: metrics
-      path: /metrics
----
-# valkey-operator-managed ValkeyCluster pods (e.g. jellyfin-valkey) get fixed
-# operator labels only -- the ValkeyCluster CR has no pod-label passthrough, so
-# they cannot carry monitoring.unkin.net/redis-exporter and need their own
-# selector. The operator's exporter sidecar also listens on :9121 with a port
-# named `metrics`.
-apiVersion: operator.victoriametrics.com/v1beta1
-kind: VMPodScrape
-metadata:
-  name: valkey-operator-clusters
-  namespace: observability
-spec:
-  namespaceSelector:
-    any: true
-  selector:
-    matchLabels:
-      app.kubernetes.io/managed-by: valkey-operator
-      app.kubernetes.io/component: valkey-node
-  podMetricsEndpoints:
-    - port: metrics
-      path: /metrics