feat: add Helm chart with GHCR OCI publish workflow

- Add charts/cloudflare-ddns/ Helm chart (env-var config, hostNetwork by default)
- Add .github/workflows/helm.yml — lint → package → push to oci://ghcr.io/timothymiller
- Update README Kubernetes section with Helm install guide (quick install, values.yaml, upgrade/uninstall)
- Keep k8s/cloudflare-ddns.yml as legacy raw-manifest fallback

charts/cloudflare-ddns/Chart.yaml

@@ -0,0 +1,16 @@
+apiVersion: v2
+name: cloudflare-ddns
+description: Dynamic DNS client for Cloudflare — keeps A/AAAA records in sync with your public IP
+type: application
+version: 0.1.0
+appVersion: "2.1.2"
+home: https://github.com/timothymiller/cloudflare-ddns
+sources:
+  - https://github.com/timothymiller/cloudflare-ddns
+keywords:
+  - ddns
+  - cloudflare
+  - dns
+maintainers:
+  - name: timothymiller
+    url: https://github.com/timothymiller