Add melange/apko build pipeline and Kubernetes manifests

- Add melange.yaml for distroless package build
- Add apko.yaml for minimal container image
- Add GitHub Actions workflow for melange/apko CI build
- Add Kubernetes manifests (deployment, service, configmap, secret, redis)
- Update Dockerfile, .gitignore, and docker-compose.yml

k8s/secret.yaml

@@ -0,0 +1,14 @@
+apiVersion: v1
+kind: Secret
+metadata:
+  name: apcupsd-client-secret
+  namespace: apcupsd
+  labels:
+    app.kubernetes.io/name: apcupsd-client
+    app.kubernetes.io/part-of: apcupsd-client
+type: Opaque
+stringData:
+  SESSION_SECRET: "CHANGE_ME_TO_A_RANDOM_SECRET"
+  # Optional — uncomment and set as needed:
+  # SMTP_PASSWORD: ""
+  # ADMIN_PASSWORD_HASH: ""