feat(loki): add single-binary loki and alloy stack

Filesystem storage on local-path-retain, 14d retention. Alloy daemonset ships k8s pod logs to loki-gateway.

loki/k8s/alloy-values.yaml

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+# Pinned chart: grafana/alloy 1.12.1 (app v1.19.2).
+# Install (deferred to deploy task, namespace prometheus):
+#   helm upgrade --install alloy grafana/alloy --version 1.12.1 \
+#     --namespace prometheus --values loki/k8s/alloy-values.yaml --wait
+# DaemonSet ships k8s pod logs (API-tailed, no hostPath mounts) to Loki.
+# Scope phase 1: k8s only, compose leftovers out.
+
+controller:
+  type: daemonset
+  resources:
+    requests:
+      memory: "128Mi"
+      cpu: "50m"
+    limits:
+      memory: "512Mi"
+      cpu: "500m"
+
+image:
+  tag: "v1.19.2"
+
+alloy:
+  configMap:
+    create: true
+    content: |
+      discovery.kubernetes "pods" {
+        role = "pod"
+      }
+
+      discovery.relabel "pods" {
+        targets = discovery.kubernetes.pods.targets
+
+        rule {
+          source_labels = ["__meta_kubernetes_namespace"]
+          target_label  = "namespace"
+        }
+
+        rule {
+          source_labels = ["__meta_kubernetes_pod_name"]
+          target_label  = "pod"
+        }
+
+        rule {
+          source_labels = ["__meta_kubernetes_pod_container_name"]
+          target_label  = "container"
+        }
+      }
+
+      loki.source.kubernetes "pods" {
+        targets    = discovery.relabel.pods.output
+        forward_to = [loki.write.default.receiver]
+      }
+
+      loki.write "default" {
+        endpoint {
+          url = "http://loki-gateway.prometheus.svc.cluster.local/loki/api/v1/push"
+        }
+      }

loki/k8s/loki-values.yaml

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+# Pinned chart: grafana/loki 7.3.0 (app 3.6.12).
+# Install (deferred to deploy task, namespace prometheus):
+#   helm upgrade --install loki grafana/loki --version 7.3.0 \
+#     --namespace prometheus --values loki/k8s/loki-values.yaml --wait
+# SingleBinary, filesystem storage on local-path-retain, 14d retention.
+# No IngressRoute: Loki is cluster-internal, queried via Grafana datasource.
+
+deploymentMode: SingleBinary
+
+loki:
+  # Multitenancy off: single-node homelab, gateway + Alloy + Grafana talk to one tenant.
+  auth_enabled: false
+  image:
+    tag: "3.6.12"
+  commonConfig:
+    # Single replica: default RF=3 would require 3 ingesters and fail all writes.
+    replication_factor: 1
+  storage:
+    type: filesystem
+  schemaConfig:
+    configs:
+      - from: "2024-04-01"
+        store: tsdb
+        object_store: filesystem
+        schema: v13
+        index:
+          prefix: index_
+          period: 24h
+  compactor:
+    retention_enabled: true
+    delete_request_store: filesystem
+  limits_config:
+    retention_period: 336h
+  rulerConfig:
+    wal:
+      dir: /var/loki/ruler-wal
+    storage:
+      type: local
+      local:
+        directory: /var/loki/rules
+
+singleBinary:
+  replicas: 1
+  persistence:
+    enabled: true
+    size: 20Gi
+    storageClass: local-path-retain
+  resources:
+    requests:
+      memory: "512Mi"
+      cpu: "200m"
+    limits:
+      memory: "2Gi"
+      cpu: "1000m"
+
+# Zeroed: unused in SingleBinary mode (chart validation requires it).
+write:
+  replicas: 0
+read:
+  replicas: 0
+backend:
+  replicas: 0
+
+gateway:
+  replicas: 1
+  resources:
+    requests:
+      memory: "64Mi"
+      cpu: "50m"
+    limits:
+      memory: "256Mi"
+      cpu: "300m"
+
+monitoring:
+  serviceMonitor:
+    enabled: true
+    labels:
+      release: prometheus-stack
+    interval: 15s
+  rules:
+    enabled: true
+    namespace: prometheus
+    labels:
+      release: prometheus-stack
+
+# Disabled: memcached caches don't fit a memory-tight single node.
+# SingleBinary works without them (slower repeated queries, fine at homelab scale).
+resultsCache:
+  enabled: false
+chunksCache:
+  enabled: false
+
+# Disabled: synthetic canary traffic + helm test pod, noise on a single node.
+lokiCanary:
+  enabled: false
+test:
+  enabled: false