feat(infra): add K3s GitOps infrastructure and Packer golden image build (#25)

### Summary of Changes

This PR introduces a declarative, GitOps-managed cloud infrastructure
for the monorepo using K3s, Flux v2, and HashiCorp Packer:

1. **Packer Golden Image Builder (`ci/packer/`)**:
- Automated Debian 12 minimal base OS image creation using QEMU builder,
UEFI firmware, GPT partition scheme, and 2M cluster size `.qcow2`
conversion.
- Cloud-init, `virtio` kernel drivers, and serial console (`ttyS0`,
115200 baud).
- Pre-installed K3s binary (`v1.31.2+k3s1`) with isolated first-boot
token and cert generation.
   - Full identity sanitization (`machine-id` and SSH host key resets).

2. **First-Boot Cloud-Init Bootstrapping
(`ci/cloud-init/user-data.yaml`)**:
- Configures K3s with `servicelb` disabled and TLS SANs for custom
domains and static IP.
- Waits for API readiness, initializes `flux-system` namespace, injects
`sops-age` secret, and triggers Flux sync.

3. **SOPS & GitOps Root Orchestration (`.sops.yaml`,
`ci/k8s/clusters/production/`)**:
- SOPS encryption configuration targeting Kubernetes secrets with `age`
key recipient.
- Flux v2 `GitRepository` and `Kustomization` manifests tracking `next`.

4. **Infrastructure & Networking (`ci/k8s/base/`,
`ci/k8s/infrastructure/`)**:
   - Dedicated `com-ermnvldmr` namespace.
- `cert-manager` HTTP-01 `ClusterIssuer` (`letsencrypt-prod` &
`letsencrypt-staging`).
- Traefik Ingress routing for `ermnvldmr.com`, `www.ermnvldmr.com`,
`docs.ermnvldmr.com`, and `analytics.ermnvldmr.com`.

5. **PostgreSQL & Applications (`ci/k8s/apps/`)**:
- PostgreSQL 16 StatefulSet on 5Gi `local-path` persistent storage with
low-memory tuning.
- Deployments for `www` (pinned `sha-6d33b71`), `docs` (pinned
`sha-91f5245`), and `umami` (pinned `postgresql-v2.14.0`) with
zero-downtime rolling update strategy.

6. **CI/CD Workflows (`.github/workflows/`)**:
- `ci - next/build-golden-image`: Workflow to build and upload
`com-ermnvldmr-debian-12-k3s-amd64-<tag>.qcow2` to static S3
`/dev/images/`.
- Updated `services-www-releases-dispatch-release.yml` and
`services-docs-next-required.yml` with GitOps deployment steps.

ci/k8s/apps/postgres/configmap.yaml

@@ -0,0 +1,21 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: postgres-config
+  namespace: com-ermnvldmr
+data:
+  postgresql.conf: |
+    # Low-memory tuned configuration for single-node K3s VM
+    listen_addresses = '*'
+    max_connections = 50
+    shared_buffers = 64MB
+    effective_cache_size = 128MB
+    maintenance_work_mem = 16MB
+    checkpoint_completion_target = 0.9
+    wal_buffers = 2MB
+    default_statistics_target = 100
+    random_page_cost = 1.1
+    effective_io_concurrency = 200
+    work_mem = 4MB
+    min_wal_size = 80MB
+    max_wal_size = 512MB

ci/k8s/apps/postgres/kustomization.yaml

@@ -0,0 +1,9 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+namespace: com-ermnvldmr
+resources:
+  - configmap.yaml
+  - secret.template.yaml
+  - pvc.yaml
+  - statefulset.yaml
+  - service.yaml

ci/k8s/apps/postgres/pvc.yaml

@@ -0,0 +1,12 @@
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: postgres-pvc
+  namespace: com-ermnvldmr
+spec:
+  accessModes:
+    - ReadWriteOnce
+  storageClassName: local-path
+  resources:
+    requests:
+      storage: 5Gi

ci/k8s/apps/postgres/secret.template.yaml

@@ -0,0 +1,10 @@
+apiVersion: v1
+kind: Secret
+metadata:
+  name: postgres-secrets
+  namespace: com-ermnvldmr
+type: Opaque
+stringData:
+  POSTGRES_DB: "umami"
+  POSTGRES_USER: "umami"
+  POSTGRES_PASSWORD: "CHANGE_ME_IN_ENCRYPTED_SOPS_SECRET"

ci/k8s/apps/postgres/service.yaml

@@ -0,0 +1,13 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: postgres-service
+  namespace: com-ermnvldmr
+spec:
+  type: ClusterIP
+  selector:
+    app: postgres
+  ports:
+    - name: postgres
+      port: 5432
+      targetPort: 5432

ci/k8s/apps/postgres/statefulset.yaml

@@ -0,0 +1,83 @@
+apiVersion: apps/v1
+kind: StatefulSet
+metadata:
+  name: postgres
+  namespace: com-ermnvldmr
+spec:
+  serviceName: postgres-service
+  replicas: 1
+  selector:
+    matchLabels:
+      app: postgres
+  template:
+    metadata:
+      labels:
+        app: postgres
+    spec:
+      containers:
+        - name: postgres
+          image: postgres:16-alpine
+          imagePullPolicy: IfNotPresent
+          env:
+            - name: POSTGRES_DB
+              valueFrom:
+                secretKeyRef:
+                  name: postgres-secrets
+                  key: POSTGRES_DB
+            - name: POSTGRES_USER
+              valueFrom:
+                secretKeyRef:
+                  name: postgres-secrets
+                  key: POSTGRES_USER
+            - name: POSTGRES_PASSWORD
+              valueFrom:
+                secretKeyRef:
+                  name: postgres-secrets
+                  key: POSTGRES_PASSWORD
+            - name: PGDATA
+              value: /var/lib/postgresql/data/pgdata
+          ports:
+            - name: postgres
+              containerPort: 5432
+          resources:
+            requests:
+              cpu: 50m
+              memory: 128Mi
+            limits:
+              cpu: 250m
+              memory: 256Mi
+          volumeMounts:
+            - name: data
+              mountPath: /var/lib/postgresql/data
+            - name: config
+              mountPath: /etc/postgresql/postgresql.conf
+              subPath: postgresql.conf
+          readinessProbe:
+            exec:
+              command:
+                - pg_isready
+                - -U
+                - $(POSTGRES_USER)
+                - -d
+                - $(POSTGRES_DB)
+            initialDelaySeconds: 5
+            periodSeconds: 10
+            timeoutSeconds: 5
+          livenessProbe:
+            exec:
+              command:
+                - pg_isready
+                - -U
+                - $(POSTGRES_USER)
+                - -d
+                - $(POSTGRES_DB)
+            initialDelaySeconds: 15
+            periodSeconds: 20
+            timeoutSeconds: 5
+      volumes:
+        - name: data
+          persistentVolumeClaim:
+            claimName: postgres-pvc
+        - name: config
+          configMap:
+            name: postgres-config