Add dev/stg/prod environments with per-env values, configmaps and secrets

- Move env-specific config into environments/<env>/{values,configmap,secret}.yaml
  for both nginx-chart and mysql-chart (dev, stg, prod)
- Make templates env-agnostic: resource names come from values
  (configMap.name, secret.name)
- nginx deployment mounts env ConfigMap and loads env Secret via envFrom
- mysql statefulset reads DB config from ConfigMap, passwords from Secret
- Remove mysql-chart/templates/secret.yaml (secrets are now per-env manifests)
- Add README with layout and deploy commands

nginx-chart/environments/prod/secret.yaml

@@ -0,0 +1,31 @@
+# ---------------------------------------------------------------------------
+# Registry pull secret used by the nginx Deployment (imagePullSecrets).
+# Replace the credentials with the real registry values, or regenerate with:
+#   kubectl create secret docker-registry harbor-secret \
+#     --docker-server=imageregistry.gen-itech.com \
+#     --docker-username=demo --docker-password=demo123 \
+#     -n prod --dry-run=client -o yaml
+# ---------------------------------------------------------------------------
+apiVersion: v1
+kind: Secret
+metadata:
+  name: harbor-secret
+  namespace: prod
+type: kubernetes.io/dockerconfigjson
+stringData:
+  .dockerconfigjson: |
+    {"auths":{"imageregistry.gen-itech.com":{"username":"demo","password":"demo123","auth":"ZGVtbzpkZW1vMTIz"}}}
+
+---
+# ---------------------------------------------------------------------------
+# Application secret for the nginx container (loaded via envFrom).
+# ---------------------------------------------------------------------------
+apiVersion: v1
+kind: Secret
+metadata:
+  name: nginx-secret-prod
+  namespace: prod
+type: Opaque
+stringData:
+  APP_ENV: prod
+  APP_SECRET: change-me-prod