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/clusters/production/flux-system/gotk-sync.yaml

@@ -0,0 +1,30 @@
+apiVersion: source.toolkit.fluxcd.io/v1
+kind: GitRepository
+metadata:
+  name: ermnvldmr-repo
+  namespace: flux-system
+spec:
+  interval: 1m
+  url: https://github.com/deytenit/ermnvldmr.com.git
+  ref:
+    branch: next
+---
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: cluster-sync
+  namespace: flux-system
+spec:
+  interval: 5m
+  targetNamespace: flux-system
+  sourceRef:
+    kind: GitRepository
+    name: ermnvldmr-repo
+  path: ./ci/k8s/clusters/production
+  prune: true
+  wait: true
+  timeout: 3m
+  decryption:
+    provider: sops
+    secretRef:
+      name: sops-age

ci/k8s/clusters/production/flux-system/kustomization.yaml

@@ -0,0 +1,4 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+  - gotk-sync.yaml