Take the observability secrets from Vault

k8s/secret.yaml held the Grafana admin credentials and, since the MCP
server landed, its service account token — gitignored, so deploying this
stack required the right file to exist on the right laptop. It now comes
from Vault through External Secrets, and nothing sensitive has to exist
locally.

A dedicated store rather than reusing vault-kong-v2: that one's AppRole
carries kong-v2-readonly, scoped to secrets/data/kong-v2/*, so it cannot
see this path — confirmed with a probe ExternalSecret that failed with
"could not get secret data from provider". Widening that policy would have
handed the Kong reader observability's secrets for no reason. So
observability-readonly and observability-eso were created in Vault,
mirroring the existing pattern exactly.

The AppRole credentials stay out of git; the ClusterSecretStore comments
carry the commands that mint them.

dataFrom.extract pulls the whole path instead of naming each key, so a new
key in Vault reaches the cluster with no edit here. The target keeps the
name every consumer already uses, so neither the Grafana Deployment nor
mcp-grafana changed — verified, neither pod restarted and the token in the
cluster matches Vault byte for byte.

secret.example.yaml no longer describes a file to create; it documents
where the keys live and how the Grafana token is minted.

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

k8s/secrets/clustersecretstore.yaml

@@ -0,0 +1,35 @@
+# Reads secrets/observability/* from Vault. Deliberately not reusing the
+# vault-kong-v2 store: its AppRole carries the kong-v2-readonly policy, scoped
+# to secrets/data/kong-v2/*, so it simply cannot see this path — verified, a
+# probe ExternalSecret against it failed with "could not get secret data from
+# provider". Widening that policy would have given the Kong reader access to
+# observability's secrets for no reason.
+#
+# The AppRole credentials are NOT in git. Created once against Vault:
+#   vault policy write observability-readonly  (read on secrets/{data,metadata}/observability/*)
+#   vault write auth/approle/role/observability-eso token_policies=observability-readonly
+#   vault read  auth/approle/role/observability-eso/role-id
+#   vault write -f auth/approle/role/observability-eso/secret-id
+#   kubectl -n external-secrets create secret generic vault-approle-observability \
+#     --from-literal=roleId=<...> --from-literal=secretId=<...>
+apiVersion: external-secrets.io/v1
+kind: ClusterSecretStore
+metadata:
+  name: vault-observability
+spec:
+  provider:
+    vault:
+      server: https://vault.sttlab.eu
+      path: secrets
+      version: v2
+      auth:
+        appRole:
+          path: approle
+          roleRef:
+            name: vault-approle-observability
+            namespace: external-secrets
+            key: roleId
+          secretRef:
+            name: vault-approle-observability
+            namespace: external-secrets
+            key: secretId