Add platform infrastructure configuration

services/observability/loki/README.md

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+# Loki
+
+This root renders `grafana-community/loki` chart `18.7.1` as one Loki
+`3.7.4` monolithic StatefulSet in `observability`.
+
+- The image is pinned to the reviewed amd64 digest.
+- Logs use the `loki` AIStor bucket through `loki-object-storage`; no root
+  credential is referenced.
+- Retention is 30 days. The WAL and working data use the dedicated 5Gi
+  Retain Local PV.
+- Gateway, canary, caches, embedded MinIO, tests, and rule sidecars are
+  disabled.
+- The only client-facing service is ClusterIP port 3100.
+
+Do not delete the PVC or bucket during rollback. Scale the StatefulSet down,
+preserve its Retain volume, and investigate S3/WAL state before reapplying.